On Sunday, the Boston Red Sox will close out their historically successful regular season, one in which they set a new franchise record for wins (107) and could very well have the MVP (Mookie Betts) and Cy Young (Chris Sale) winners on their roster.

At this point, success for the 2018 Red Sox will not be measured with wins and losses or awards. When you're this good, you have to win the World Series to validate it all, otherwise you risk becoming an afterthought like the 2001 Mariners rather than be considered among history's best teams like the 1998 Yankees. That's how these things tend to go. Win a title or be forgotten.

For the Red Sox to have their best chance at a World Series this year, they're going to need Sale to be at his best in October, and right now that seems like a dicey proposition. On-and-off shoulder trouble have limited Sale to five starts since the end of the July and he hasn't completed five innings in a start since Aug. 12. Last time out he allowed three runs and needed 92 pitches to complete 4 2/3 innings against the lowly Orioles.

Sale's velocity has been trending the wrong way in recent weeks as well. Here is his game-by-game average velocity the last two seasons:

Chris Sale's fastball velocity has been way down lately. Brooks Baseball

Sale made his final start of the regular season this past Wednesday and his average fastball velocity in that game (90.2 mph) was his lowest ever in a big league game. His velocity was down so much that the Statcast algorithm classified several fastballs as changeups. That's never a good sign. Especially not after two shoulder-related trips to the disabled list.

The Red Sox insist Sale's missing velocity is being caused by faulty mechanics, not the shoulder trouble that sent him to the disabled list twice in the second half. Here's what Sale and manager Alex Cora told reporters, including Jason Mastrodonato of the Boston Herald, a few days ago:

"Just not really driving off my lower half and really create that torque I have in the past," he said Wednesday. "We've got extended time now to kind of figure out what we need to do and we'll go from there."

Cora said the team is confident Sale's shoulder is healthy.

"I don't feel that's the reason," Cora said yesterday. "We've been talking about it the whole time and we don't feel it's the shoulder. His mechanics were way off in the first outing, probably, they got better, then all of the sudden last one it wasn't there. But we don't feel it has anything to do with the shoulder."

Red Sox president of baseball operations Dave Dombrowski has already said Sale will start Game 1 of the ALDS next Friday, when they'll face the winner of the AL Wild Card Game between Yankees and Athletics. Because Sale last started Wednesday, he'll throw at least one and possibly two side sessions before the ALDS begins, giving him a chance to solve his mechanical problem.

For what it's worth, September has historically been Sale's worst month throughout his career (3.78 ERA and .747 OPS against), which has led to speculation he simply wears down. He's tall and slender, and at age 29, he now has several years worth of wear and tear on his body. All those innings and all those pitches could be manifesting themselves in his missing velocity now.

The Red Sox do have rotation depth behind Sale in David Price, Rick Porcello, Nathan Eovaldi, and Eduardo Rodriguez. Clearly though, their best chance to win the World Series involves having a healthy and productive Chris Sale atop the rotation. Sale can still be effective with a 90 mph fastball. Can he dominate with that velocity? Based on his last start, the answer seems to be no.