For Red Sox reliever Matt Barnes, anything that could go wrong did go wrong in the last six weeks

Matt Barnes (right) was left off the Red Sox' ALCS roster.Jim Davis/Globe Staff

HOUSTON — Through July, the 2021 season was inarguably the greatest in the 10-year professional career of Matt Barnes. He emerged as an All-Star closer whose dominance played a huge role in the Red Sox’ surprise emergence as a contender. He signed a two-year extension just before the All-Star break, and enjoyed living the good life, confident nearly every time he took the mound he had the high-90s fastball and wipeout curveball to mow through opposing teams.

And then came August. Barnes (like many relievers) hit a wall while trying to endure the jump from a 60- to 162-game season, lost his job as a closer, and then somehow saw his season continue to get worse.

“The first four to five months, I mean, I knew I could go out there and put 98 wherever I wanted, whenever I wanted with a breaking ball,” said Barnes. “And then I go through a stretch where I’m throwing a ton of games in a really short span, kind of lose it, try to find a way to create more — which is never the right answer, but it just, it’s hard not to do that.

“So then we start trying to figure out, ‘OK, how do I get back?’ As soon as we’re getting close, I get COVID,” said Barnes, who suffered a breakthrough positive infection at the end of August. “I have COVID for three weeks and wasn’t completely corrected [on the mound]. So now when I come back, it doesn’t just come back. I’m still working. And then all of a sudden I cut part of my thumb off.”

Come again?

In late September, Barnes was chopping a pepper while making an omelet when he sliced off the tip of his left thumb. He’s wearing a bandage on the digit, with a hard plastic casing inside his glove so he can catch the ball without pain.

“The last six weeks, I feel like everything just has been crazy,” said Barnes. “The first four months, five months, everything was perfect. The last six weeks anything that could have gone wrong has gone wrong. It’s just been a crazy year. It really has.”

Barnes is less concerned about the thumb than about the struggles that resulted in his exclusion from the ALCS roster. He lost his job as closer in late-August, tested positive for COVID-19 shortly thereafter, and allowed two runs in five innings over six outings to end the regular season, mostly in low-leverage spots.

The Sox initially left him off the ALDS roster against Tampa Bay, but added him back when Garrett Richards landed on the injured list with a hamstring injury. But for the ALCS against the Astros, the team again left him off.

The development is unquestionably disappointing for a pitcher who was the most reliable Red Sox reliever in the 2018 postseason (including in the ALCS against the Astros, when he pitched in all five games, allowing one run on one hit in 4⅓ innings). But Barnes recognizes his performance left manager Alex Cora and the team little choice.

“It’s really difficult [to be left off the roster],” said Barnes. “You’ve been grinding for the last seven months with these guys. And obviously you want to continue to do your part. But it’s about putting the best team that A.C. and the front office thinks gives us the best chance to move on to a World Series. Regardless of how frustrated or mad I am about it, right now it’s bigger than me.”

After his omission — and subsequent addition — in the ALDS, Barnes understands that circumstances can shift quickly and that he needs to remain sharp in case the Red Sox do need him, either moving forward in the ALCS or potentially in the World Series.

“This is tough, but like I said, it is what it is right now. My job is to stay ready as best I can, cheer these guys on, and hopefully move on,” said Barnes, who is watching the games from the unfamiliar vantage point of the dugout. “I have to stay ready. You never know. I’d be doing a disservice to the guys on the field if I don’t stay ready.”