After a season-opening road trip -- a long, miserable, soul-searching trip -- the Boston Red Sox already have learned what the 18 previous World Series winners learned: In the current era of baseball, repeating as champion is a formidable task.

Since the Yankees won three World Series in a row from 1998 to 2000, no team has repeated. Only two champions managed to return to the World Series -- the 2000 Yankees and the 2008 Phillies. (Three other teams have played in back-to-back World Series: the 2010-11 Rangers, 2014-15 Royals and 2017-18 Dodgers.) Nine of the 18 champions failed to make the playoffs the following season. As Ron Washington might say about going back-to-back, "It's incredibly hard."

The Red Sox began their title defense with an 11-game road trip to Seattle, Oakland and Arizona, not exactly Murderers' Row considering the Mariners and Diamondbacks lost or traded away most of their best players in the offseason. The Red Sox went 3-8, and it wasn't an unlucky 3-8. They were outscored by 26 runs, the worst run differential in the majors. They lost games by scores of 12-4, 7-0 and 15-8. The starting rotation has a 8.57 ERA, worst in the majors. The A's shut them out in consecutive games.

It was an ugly start that puts a bit of damper on Tuesday's home opener and pregame ring and flag-raising ceremony. After all, Boston fans have grown to expect only the best -- at all times -- from their teams. Still, I would expect the fans to greet the Red Sox mostly with cheers on Tuesday. Flags do fly forever.

Some have blamed the slow start on the Red Sox limiting the innings for their starters in spring training, an understandable approach given all the work they had in the postseason. Still, the first two trips through the rotation suggested the starters were perhaps rusty from the lack of work in Florida and the 1-0 win to close out the road trip Sunday actually came courtesy of a bullpen game, with Hector Velazquez starting and pitching three innings.

"We played in the last game of the year, so there's obviously a longer effect," Chris Sale told ESPN's Pedro Gomez over the weekend in Phoenix, "but like I've said, we're not going to say we're making excuses. I can't wait to get to Fenway. It's part of the business. It's what we signed up for. At a certain point, we have to show up and win."

All eyes will be on Sale on Tuesday against the Blue Jays as he makes his third start. His first game against the Mariners was one of the worst starts of his career with seven runs in three innings. He allowed just one run against the A's in six innings, but he also struck out just one batter. With his velocity down, he reverted to throwing a lot of breaking balls.

Sale just signed a five-year, $145 million contract extension and the Red Sox wouldn't have shelled out that money without being comfortable with his medical reports, so the hope has to be that Sale is simply easing into the season. It's worth noting that he was sitting 93-94 mph last April with his fastball before ramping up and sitting in the upper 90s in June and July, when he destroyed opponents. He then landed on the injured list in August.

Obviously, the Red Sox were likely to have fewer than the club-record 108 wins they had last year no matter what kind of start they had. During the divisional era since 1969, 12 previous teams won at least 100 games and the World Series. Here's how those 12 teams did the following year:

Better record: 1 (2017 Astros)
Same record: 1
Worse record: 10
Won division: 6
Missed postseason: 5
Won World Series: 3
Average win regression: 10.3

The three teams went on to win 100 games, then repeat as World Series champs: the 1975-76 Reds, 1977-78 Yankees and 1998-99 Yankees. If they Red Sox can follow up with another title, they should deservedly go down as one of the best teams of all time.

But is it possible?

Repeating is even more difficult in the wild-card era (since 1995), due to the extra round of the playoffs. Now you have to beat three teams in the postseason instead of two, and that's assuming you've avoided the wild-card game. Winning six straight postseason series -- no matter how good you are -- is a Herculean task, which puts the Yankees' streak of 11 straight postseason series wins from 1998 to the 2001 World Series in remarkable perspective.

Another reason we've gone 18 seasons without a repeat champion is that several of the champs in this stretch haven't exactly been powerhouses. Good enough to get hot in October and win a World Series, not good enough to make it back to the playoffs the next season. Consider a few of these World Series winners:

• 2002 Angels: They fell from 99 wins to 77, the second-biggest decrease of the 18 teams. That team milked the last good season from Kevin Appier, and Jarrod Washburn and Ramon Ortiz had career seasons.

• 2003 Marlins: The Marlins won the wild card with 91 wins. That offseason they traded Derrek Lee and lost Ivan Rodriguez as a free agent and fell to 83 wins and haven't returned to the postseason since.

• 2006 Cardinals: St. Louis sneaked into the playoffs with just 83 wins courtesy of a weak division. They had only three players exceed 2.0 WAR -- Albert Pujols, Scott Rolen and Chris Carpenter. Not surprisingly, they fell to 78 wins the next year.

• 2010 Giants: The Giants won 92 games and had a strong rotation, but fell to 86 wins in 2011. It wasn't just because of Buster Posey's injury. Their two best position players in 2010 had been Aubrey Huff (5.7 WAR) and Andres Torres (5.3), who combined for just 0.8 WAR in 2011.

• 2013 Red Sox: The Red Sox were certainly great for one season, winning 97 games and outscoring their opponents by 197 runs, but it was kind of a fluke season, with several one-season wonders (remember Mike Carp and his .885 OPS?) or older guys near the end (Shane Victorino, Ryan Dempster). They lost 93 games in 2012, 91 in 2014 and 84 in 2015.

• 2014 Giants: They won 88 games and the wild card, and then Madison Bumgarner had the October to end all Octobers. The Giants won 84 games in 2015.

The past 18 World Series winners declined an average of 6.7 wins. If the Red Sox decline only 6.7 wins, that will be good! That will still mean 101 or 102 wins, which will get them back in the postseason.

The stars will carry them

I was curious how important it is to have a strong base of stars. Do World Series teams decline because they get less value from their best players or less value from the supporting cast? I took the top four players in WAR from the World Series winners and compared them to the team's top four players the following season (not necessarily the same four players).

Overall, a team's WAR from its four best players dropped 1.7 wins, so this explains only 25 percent of a team's decline the following seasons.

There's some good news for the 2019 Red Sox. Here are the top six foursomes from the World Series winners (plus the Red Sox):

2001 Diamondbacks (Randy Johnson, Curt Schilling, Luis Gonzalez, Reggie Sanders): 30.1 WAR

2018 Red Sox (Mookie Betts, Chris Sale, J.D. Martinez, David Price): 28.5 WAR

2016 Cubs (Kris Bryant, Jon Lester, Anthony Rizzo, Kyle Hendricks): 23.9 WAR

2008 Phillies (Chase Utley, Jimmy Rollins, Shane Victorino, Cole Hamels): 23.2 WAR

2017 Astros (Jose Altuve, Carlos Correa, George Springer, Dallas Keuchel): 23.1 WAR

2007 Red Sox (Josh Beckett, David Ortiz, Mike Lowell, Kevin Youkilis): 22.6

2009 Yankees (Derek Jeter, CC Sabathia, Mark Teixeira, Robinson Cano): 22.6

The previous six teams with the best foursomes all returned to the postseason. Those six dropped an average of only 1.8 wins the following seasons (with the 2016-17 Cubs having the biggest drop-off from 103 to 92 wins). If Betts, Sale, Martinez and Price perform close to what they did in 2018, the Red Sox are a good bet to bounce back from this 3-8 start.

No newcomers

The Red Sox are the third straight 100-win team to win the World Series. The 2017 Cubs suffered from a self-admitted World Series hangover and were under .500 at the All-Star break at 43-45. They recovered to go 49-25 in the second half. The Astros, on the other hand, got off to a great start at 20-10 last April and were 49-25 through June 18 after a 12-game winning streak (although the Mariners were hot on their tail at just two games back).

The Red Sox, like the Cubs, essentially brought the same team back. The Astros, however, had two significant new additions: Justin Verlander (who had made only five regular-season starts for the team in 2017) and Gerrit Cole. Because of the addition of those two, the Astros were able to withstand a big drop in runs scored and still win two more games than in their championship season.

The Red Sox will have Nathan Eovaldi and Steve Pearce for the entire season, but otherwise have the same team minus Craig Kimbrel and light-hitting catcher Sandy Leon. Maybe a little new blood would have helped.

Of course, that's just speculation. The Red Sox have played only 6.8 percent of the schedule. It was a bad 6.8 percent and puts them five games behind the Rays, and in what projects as a tight AL East race, that means it is more likely Alex Cora will end up having to push his starters hard during the summer.

That's down the road. For now, there's one last chance to celebrate maybe the best Red Sox team in history. Then it's time to move on and start winning some games.