Coach Peter DeBoer was speechless as he walked into the Vegas Golden Knights' dressing room Monday night after Game 5 of the NHL's Western Conference finals.

"I didn't prepare something to say to them tonight, because I just didn't think we'd lose," he said.

Lose they did.

Dallas Stars forward Denis Gurianov's goal at 3 minutes, 36 seconds of overtime gave his team a 3-2, come-from-behind victory and eliminated the Golden Knights from the postseason. Dallas advanced to the Stanley Cup Final for the first time since 2000.

"We all feel like this is a wasted opportunity," said forward Reilly Smith, an original Golden Knight from the team's first season in 2017-18. "This is probably the best, most skilled team that I played on in my career. To win the Stanley Cup was our one goal. We didn't want anything short of that. Definitely feel defeated."

Vegas entered the restarted NHL season with its eyes on the Cup. The Golden Knights were first in the Pacific Division. They had aggressively augmented their roster during the season; firing coach Gerard Gallant after a 24-19-6 start, and hiring DeBoer, the very coach who defeated them in Game 7 of last postseason's opening round while with the San Jose Sharks; and trading for Kings defenseman Alec Martinez and Blackhawks goalie Robin Lehner at the deadline.

They eliminated Chicago in the quarterfinals in five games, then outlasted the Vancouver Canucks -- and the brilliant goaltending of Thatcher Demko in the last three games of the series -- with a Game 7 victory in the semifinals. They entered the Western Conference finals against the Stars as the odds-on favorite in the sportsbooks to win the Stanley Cup.

What went wrong?

"They scored timely goals. It was a tight series. Our team probably outplayed them for 90% of it, but that's what cost us: We weren't scoring, and they were," Smith said. "The last eight games, it felt like we were cursed around the net. Nothing was going in."

Dallas outscored the Knights 9-8 for the series played in Edmonton, Alberta, as part of the league's bubble amid the coronavirus pandemic.

"This game, a lot like the rest of the series, we couldn't get that next goal to extend [the lead]," DeBoer said. In Game 5, Knights center Chandler Stephenson scored at 8:14 of the first period on a breakaway for a 1-0 lead. Smith snapped a shot high on Stars goaltender Anton Khudobin to give Vegas a 2-0 lead just 15 seconds into the third period. The Knights had been 10-2 in the playoffs when scoring the first goal. Between the regular season and the playoffs, the Knights were 36-1-4 when leading after two periods.

But Dallas started picking up the pace in the third period, and that effort manifested in Jamie Benn's goal at 9:54. Defenseman Esa Lindell passed the puck from behind the net, it deflected off of winger Alexander Radulov and then right to Benn, who snapped a wrist shot to cut the lead in half.

"There's no panic in that dressing room. We're a resilient group," Benn said. "We enjoy the challenge."

The Stars tied the game with Vegas forward Alex Tuch in the penalty box for tripping. Defenseman John Klingberg got a shot through traffic, Lehner made the save and Joel Kiviranta -- whose hat trick won Game 7 in overtime for the Stars against Colorado in the semifinals -- slapped home the rebound to tie the game at 16:13 of the third.

In overtime, the game turned on a crucial and unfortunate mistake from rookie defenseman Zach Whitecloud, who attempted to bat the puck away from a racing Dallas forward and accidentally sent it over the glass for a delay-of-game penalty at 2:15. Gurianov would score the series clincher a few moments later.

"I just feel terrible for the kid," DeBoer said. "It's such a s---ty penalty to begin with. For that type of penalty to decide a game just doesn't make sense to me. But for him, he's got nothing to hang his head about. He played his ass off. He's got a bright future ahead of him here."

In theory, so do the Knights. This is their second trip to the conference finals in three years of existence, having lost in the Stanley Cup Final to Washington in their inaugural season. Outside of a few unrestricted free agents -- including Lehner, although it's expected he'll return -- the Golden Knights' roster could be intact for another run next season.

"The goal of this team is to win the Stanley Cup and they're right in that window," DeBoer said. "It's the toughest trophy in hockey to win. It's an unbelievably tough road. We've gotta learn some things about what works in the playoffs and how to score in the playoffs."

That's especially true for the team's top offensive players. Dallas received production from stars such as Benn, Radulov and Joe Pavelski in the series. The same couldn't be said for the Knights' top scorers.

DeBoer noted one moment in the third period of Game 5, after Dallas cut the lead to 2-1 and Vegas forward and leading scorer Max Pacioretty -- who had just one assist in his last eight playoff games -- couldn't convert a breakaway chance.

It went beyond Pacioretty. Smith's goal was his first in 11 games. Linemate Jonathan Marchessault was without a goal during that span. Mark Stone, who battled an injury in Game 5, had one goal in nine games.

"We could never get that next goal to get out in front enough," DeBoer said. In the end, that lack of timely scoring cost the Golden Knights their most important goal. "We're not happy losing in the conference final," DeBoer said. "That wasn't the goal when we came here."