HOUSTON -- President of baseball operations Dave Dombrowski and ex-Red Sox manager John Farrell left Matt Barnes off the 2017 ALDS roster after he posted a 5.59 ERA (9.2 innings, six earned runs) during September.

"It was definitely frustrating last year but it's water under the bridge," Barnes told MassLive.com. "We're focused on now. We're in the ALCS trying to make a push. My job is to get outs and give up no runs."

Barnes hasn't given up any runs this postseason. He has pitched 4.2 scoreless and hitless innings. He has allowed three walks and has struck out three.

The righty struggled again during the second half this season. He posted a 7.89 ERA (14.2 innings, 13 earned runs) the final two months. He also dealt with hip inflammation in September. But manager Alex Cora never lost confidence in him. He always said Barnes would be important during the playoffs.

The Red Sox and Astros play Game 3 of their best-of-seven ALCS on Tuesday at Minute Maid Park. The series is tied 1-1.

Barnes is not using last year's snub as motivation.

"I don't think about last year," Barnes said. "I'm not trying to prove anybody wrong. I'm going out there just trying to do my job."

The Red Sox bullpen has done its job this October so far.

Barnes and fellow setup man Ryan Brasier both have combined for 9 scoreless innings, allowing just one hit. They have scattered seven walks and struck out eight.

Joe Kelly and Heath Hembree, who mainly have pitched with the Red Sox behind or tied, have allowed just one unearned run, two hits and four walks while striking out four in 7.2 innings.

In late September, Barnes told MassLive.com he was "very confident" the Red Sox bullpen could do the job in the postseason. "I don't think anybody in this room has a doubt," he said.

The Red Sox still need seven more wins, but Barnes is right so far.

What made him so confident?

After all, Boston's bullpen posted a 4.84 ERA and 4.52 FIP during September. It recorded a 4.32 ERA and 4.46 FIP during the second half. Boston tied for the second most blown saves (12) in the big leagues during the second half.

"For the majority of the year, we were on the best bullpens in the league," Barnes said. "I still think we finished top five in the league in bullpen ERA. In 162 games, guys are going to struggle. The best players on the planet are going to struggle. We just happened to hit it where everybody kind of struggled at the same time. So it made it look that much worse. If you look down there, there are guys with electric stuff. Everybody's got electric stuff. And we have Craig Kimbrel closing the game in the ninth. Any time you have that in the backend, it makes you even more comfortable.

"We've got guys with playoff experience," Barnes added. "We've got a few guys that have pitched in the World Series. And as a team we've kind of been there the last couple of years. When you go to war with these guys for eight months, you kind of know who they are. You know their character. You know what they're capable of. That kind of confidence never wavered."