ST. LOUIS -- The Boston Bruins and St. Louis Blues have been called mirror images of each other, from their roster construction to their style of play. But the reflections of centers Patrice Bergeron and Ryan O'Reilly would be best found in a funhouse mirror. You can make out the broad similarities, but they're anything but identical.

"Yeah, they're similar for sure," Blues coach Craig Berube said. "I think it starts in the faceoff circle with both of them. They're very good faceoff guys and play a 200-foot game. They both work extremely hard. Bergeron, he's been here before. Ryan O'Reilly is new to it, but he's obviously been our best player arguably all year long. So it's a great matchup, to be honest with you."

Bergeron and O'Reilly are both finalists for the Selke Trophy, given to the NHL's top defensive forward. In many ways, that's where the similarities end.

Professionally, Bergeron is the more lauded of the two. Considered one of the best defensive centermen in NHL history, he has won the Selke four times and been a finalist in eight straight seasons, including this one. While his defensive acumen was always appreciated, O'Reilly was just invited to the Selke party for the first time as a finalist, along with Bergeron and Vegas winger Mark Stone. O'Reilly's only previous award win came in 2014 with the Lady Byng Award for gentlemanly play after a season in which he had just two penalty minutes in 80 games.

Aesthetically, Bergeron, 33, is a well-groomed Quebecois who wouldn't look out of place in a menswear catalog. O'Reilly, 28, is an unkempt Ontarian whose neck-consuming beard has made him one of the most instantly recognizable Blues away from the rink.

From a prestige standpoint, Bergeron has a Stanley Cup ring and is seen as a primary reason the Bruins have made the Stanley Cup Final three times since 2011, having played his entire career with the team. O'Reilly is on his third NHL team and just made it past the first round for the first time. Until recently, he thought he was the reason his teams always lost.

One is the player everyone wants to be. The other is a player finally figuring out who he is.

This never gets old for Patrice Bergeron.

Not after two Olympic gold medals, world championship gold, World Cup of Hockey gold, world junior gold, two conference titles and the Stanley Cup championship. The anticipation of a series such as the one he's in against St. Louis never feels ordinary.

"The day when there will be no more adrenaline, I will retire," he said on the eve of Game 1. "This is what you are looking for as an athlete. You want to push your limits. Adrenaline, stress and butterflies, you have to manage it the right way to use it to your advantage. These are very rewarding experiences. I put it in my treasure chest."

We're not sure where Patrice Bergron's treasure chest is located. We can report that he doesn't keep his secret formula for faceoffs in his locker stall, according to teammate Charlie Coyle.

"I wish, I wish," Coyle said, laughing. "But I ask him questions, about playing against a certain guy or about what's working or not working. It helps."

Coyle met Bergeron when he was around 12 years old and playing in a hockey tournament at Bridgewater Arena, about 45 minutes from Coyle's hometown of Weymouth, Massachusetts. (Perhaps you've heard this geographic trivia about Coyle once or twice or 10,000 times during the Bruins' playoff run.) It was during the 2005 NHL lockout, and Bergeron was skating with the AHL Providence Bruins. After the game, he met Coyle and his teammates, and the young future NHLer was starstruck for life.

"He was a young guy, but he seemed really old compared to us," Coyle said.

Fast-forward to the 2019 trade deadline, and Bergeron was the first Bruin to call Coyle after the Minnesota Wild moved him to Boston in a deal for Ryan Donato. It was hours before the Bruins were getting ready to play, and Bergeron took the time to welcome Coyle, who was back to being that 12-year-old for a moment.

"I've been watching him for a while, and playing against him through the years was a nightmare," Coyle said. "Great stick. He's always on you. Not the quickest guy. Not the strongest guy. He knows what he's good at, and he does it so well.

"Just going against him in practice, that helps too. For him to be that good defensively and be so good offensively ... it's crazy."

There are many reasons the Boston Bruins are consistent contenders, but the primary one is veteran leadership and the culture that's born from it. Harvard University wishes it had educators like the Bruins have in Bergeron and Zdeno Chara. Defensemen Torey Krug, Brandon Carlo and Charlie McAvoy have all grown from playing with Chara. A collection of young forwards have learned by emulating Bergeron. In both cases, these award-winning all-stars are as revered off the ice as they are on it.

Boston center Sean Kuraly was asked what he has learned from Bergeron. "Oh man, get the laundry list out," he said. "I think the biggest thing about Bergy is his consistency and the way he approaches every single day. You come in for practice on maybe one of those 11 days in our break, and maybe it's a slow day, and him and [Brad Marchand] and Zee are going all-out. It's full-go. I think the biggest thing for Bergy is just how he approaches every single day, and he's just such a pro with it, and all of his talent doesn't hurt either. How he really does combine his talent with how hard he works is really impressive."

Bergeron's value to the Bruins was never more evident than in Game 3 of the Stanley Cup Final. In scoring a power-play goal midway through the first period, he managed to quiet the Blues' raucous crowd, get himself going offensively, start a 4-for-4 night on the power play and give Boston the start it needed.

"We knew it was going to be a loud building. A good start was important," he said. "I think you rely on the experience. Try to help the young guys on what to expect."

Bergeron led by example, and the Bruins followed. As Charlie Coyle said, that's just how it is in Boston.

"He's such an honest player. He does everything so good, everywhere on the ice," Coyle said. "You root for people like that."

For a while, Ryan O'Reilly thought he was the problem.

He had played 651 regular-season games in the NHL, and only 13 in the postseason, all with the Colorado Avalanche. His three seasons with the Buffalo Sabres were disastrous from a team perspective, as the Sabres began a "rebuild within a rebuild" after his second season. His tenure ended with the stunning revelation that he had "lost the love of the game multiple times" during last season.

Blues GM Doug Armstrong, who traded for O'Reilly last summer, was never concerned about him losing his smile.

"That honestly gave me zero pause. When you're part of an organization that's not having success, you probably -- he was speaking from the heart. He was frustrated. He wanted more from himself," he said. "I've had an opportunity to work with him internationally, I know what the man's made of. You can even go back to the [NHL combine]. We would say to players, 'Who is the hardest guy to play against?' And his name kept always popping up. We should have drafted him."

In fact, when O'Reilly got the trade call from Armstrong, his message was, "Thank you for bringing me in ... let's go win a Cup."

Then the St. Louis Blues started losing. And losing some more. So many losses that they ended up in the NHL's basement as late as January.

"It was frustrating. I was coming off a bad year, I come to a great team, and then they get off to a bad start. I was worried I was a big part of why they were losing -- that I had to something to do with it," he said.

O'Reilly spoke to his father, Brian, a sports performance coach who consults with the San Jose Sharks. He asked him if, perhaps, he were the problem. His father gave him this advice: Wait it out. Be patient. This was a new team, with a few key additions from the previous summer joining O'Reilly on the Blues. It was going to take time to come together.

It eventually did, in one of the more dramatic turnarounds in recent NHL history.

"It's amazing how things turned out. It truly is a rollercoaster ... you go through this massive run, and you're not sure if there's going to be changes, and they stick with us, and we stick together. We keep going, and we find a way to win. Then you win one series, and then another and another," O'Reilly said, motioning with his hand.

"At times, I have to pinch myself. It's weird. It doesn't feel like June. It just feels like I've been playing hockey. But around this time, I'm usually resting. Doing nothing. Away from the game. It's what the dream is: to be in these scenarios. On my off days, I try to stay away from hockey. Clear my head. But it creeps into your head sometimes. You have to calm yourself back down."

Through the Blues' early struggles, O'Reilly was consistently their best player. He played in all 82 games, posting the best points-per-game average (0.94) of his career and tying his career best of 28 goals, despite starting less than 50 percent of his even-strength shifts in the offensive zone. Defensively, he had an expected goals percentage of 57.57 and was a plus-24 in goals at 5-on-5.

"Just an all-around great two-way center. The kind of player that you need to go far and succeed," Blues teammate Tyler Bozak said. "I learned that playing against him, and honestly playing with him you realize that he's better than you even thought. Especially with how hard he works. I had heard about his work ethic and how he takes care of himself off the ice. But to see it is impressive. He's one of the first guys on the ice at practice [and] one of the last guys off."

Like Bergeron, he leads by example.

"Every time you touch the ice, work ethic is the most important thing, when you get a chance to practice and work on the things you're struggling with," he said. "I learned from my dad at a young age that you have to put in the time. It's something that builds confidence in me. Practicing those uncomfortable plays. The more time I put in, the better I feel coming into the game. We have some young guys here who like to work. They give me energy as well."

O'Reilly has that Sidney Crosby-esque thing where if a play goes wrong during a game, he'll take it apart and put it back together in practice.

"If there's a play last game that I mishandled or I didn't see what I wanted to see on it, I take some reps on that. So if it happens again, I'm not worried about it," he said.

Sometimes you have to strip hockey down to its basics, such as timing, patience and persistence. That's how you learn from your lowest moments -- or, in the case of O'Reilly, learn that you aren't the reason they happen.

"I have the greatest job in the world," he said. "But losing sucks. Losing is the worst part of it. To win is the best part of it."

As different as they are, that holds true for both Ryan O'Reilly and Patrice Bergeron.

Berube and Bruins coach Bruce Cassidy haven't given Bergeron and O'Reilly much head-to-head action through three games of the Stanley Cup Final. They barely see each other at 5-on-5. The battle of two of the best defensive centermen on the planet has been fought in the abstract and the intangibles.

"Obviously, he's the best two-way player in the game today," O'Reilly said of Bergeron before the series. "The thing I like about our team is our depth. We have a lot of guys who can play hard."

When he does see Bergeron on the ice?

"I think, 'I gotta move, I gotta get away. I need to escape.' Smart players are always in the right position," O'Reilly said.

One of the two will hoist the Stanley Cup at the end of this series. O'Reilly could create a legacy. Bergeron could further cement one. And if they fall short, they've learned that these experiences are the ones you learn from and the ones you can use to help others learn.

"You try to use your experience in great moments, I want to use it as best as I can. I have exceptional and unforgettable memories of our win in 2011. For 2013 [losing in the Cup Final], it was a more difficult moment. But I learned from both experiences," Bergeron said. "I would say that I may have grown up more in the Final defeat. I have said it often since the beginning of the series. I take the days one at a time. I stay in the moment."