Matt Barnes has been a mainstay in Red Sox’ bullpen

The Red Sox have won all 21 games when Matt Barnes has pitched the eighth inning.Matthew J. Lee/Globe Staff

HOUSTON — Given the medical misfortunes encountered first by Carson Smith and then Tyler Thornburg, it’s probably time the Red Sox stop trying to trade for relief pitchers to use in the eighth inning.

Besides, Matt Barnes has taken hold of the job.

The righthander, who turned 27 on Saturday, worked a scoreless eighth inning in Friday night’s 2-1 victory against the Astros. Barnes has appeared in the eighth inning 21 times this season with the Sox winning all of those games.

Barnes has a 3.16 earned run average overall, 2.12 in the eighth.

“I just pitch. Whatever the role is, I don’t focus on that,” Barnes said. “If I go out there and do my job, that takes care of itself.”

Bullpens work best when the pitchers know their roles and Barnes has become the primary setup man for Craig Kimbrel.

“There’s a little bit of something about Matt that doesn’t seem to get him too riled up about much. He’s able to execute and pitch with maybe some flat-line emotion that serves every guy well in those tight spots,” manager John Farrell said before Saturday night’s 7-1 loss.

Barnes has studied how Kimbrel prepares for games and gone to the closer for advice on how to approach certain hitters.

“You can learn a lot down there talking to people,” he said. “This season has been a step forward for me.”

Barnes was a first-round draft pick out of UConn in 2011 and was tried as a starter before converting to the bullpen at the end of the 2015 season.

As a reliever, he has averaged 9.5 strikeouts per nine innings.

“This year more than any that he’s been in the big leagues, he’s shown consistent ability, particularly with the curveball, to get lefties out,” Farrell said.

“His combination of [fastballs] on the top of the zone and the breaking ball is a good complement. He feels comfortable with those late-inning situations. The strikeout ability has been there.”

Barnes purchased a home near the team’s spring training complex in Fort Myers, Fla., last year. Living there, he said, helped improve his performance.

“I was able to do a lot of shoulder work with the trainers and strength coaches all winter,” Barnes said. “I was ready to go from the start of spring training.”

There have been some bumps. Barnes was suspended four games for throwing at Baltimore’s Manny Machado on April 23. He also twice missed games for personal reasons, once following the death of his grandmother.

But when he’s on the mound, it has been a secure feeling.

“He’s been very reliable, very dependable. When you can attach those two words to players, you’re in a really good place,” Farrell said.

Long partnership

Dustin Pedroia and Xander Bogaerts have been in the lineup together for 357 games going back to 2013. It’s the most for a Red Sox second baseman and shortstop combination since Jody Reed and Luis Rivera played 356 games together from 1989-92.

Prior to that, you have to go back to Mike Andrews and Rico Petrocelli playing 457 games together from 1966-70.

“It’s been nice,” said Pedroia, who played with a rotating cast of shortstops over the first seven years of his career.

“Bogey’s improved every year and we work well together.”

Pedroia said his play at second base isn’t really affected by who plays shortstop. But the chemistry it sometimes takes to turn a double play can be.

“If we can, we turn it. I put us up there with anybody,” he said.

Ramirez out again

Designated hitter Hanley Ramirez was out of the lineup for a second straight night with what the team said is a muscle spasm on the right side of his neck.

Farrell said the injury is not related to Ramirez playing nine innings at first base in Philadelphia on Thursday. Nor is it related, he said, to the right trapezius muscle strain that caused Ramirez to leave the May 10 game in Milwaukee, when he started at first base.

But Ramirez has played two games at first base this season and so far has missed a total of five starts in the aftermath of those games.

Medical ward

The Sox announced that Thornburg had successful surgery to treat thoracic outlet syndrome in his shoulder. The surgery was done on Friday in St. Louis. But that was all they revealed.

Farrell said he did not know whether Thornburg had to have a rib removed as part of the procedure. President of baseball operations Dave Dombrowski also offered little information.

“I can’t say anything yet because we haven’t talked to him about the situation,” Dombrowski said. “I’m not at liberty to discuss it.”

Remember Robbie Ross Jr., lefthanded reliever, long hair, pitched in 108 games from 2015-16? He has been on the disabled list since May 19 with elbow inflammation and still hasn’t been cleared to throw, according to Farrell.

The Sox have been disenchanted with Ross since spring training. He then had a 7.00 ERA in eight games.

Numbers game

The Astros, who have been in existence since 1962, have as many retired numbers as the Red Sox, who started play in 1901.

Not counting Jackie Robinson’s No. 42, which is retired throughout the game, Houston has retired nine numbers. Hall of Famers Nolan Ryan, Jeff Bagwell, and Craig Biggio are no surprise. But the Astros also recognized Jose Cruz, Larry Dierker, Mike Scott, Don Wilson, and Jimmy Wynn along with Jim Umbricht, a pitcher who died of cancer in 1964 after two seasons with the team.

Cruz, Dierker, Scott, Wilson, and Wynn combined for nine All-Star appearances with the Astros over 55 seasons.

The Red Sox also have nine retired numbers. Outside of Johnny Pesky, all are Hall of Famers: Wade Boggs, Joe Cronin, Bobby Doerr, Carlton Fisk, Pedro Martinez, Jim Rice, Ted Williams, and Carl Yastrzemski.

The Sox will add a 10th on June 23 when David Ortiz’s No. 34 is retired.

Roster move on deck

The Sox will retain an extra relief pitcher through Monday’s game at Kansas City. With rookie Hector Velazquez starting, they want the depth. The plan is to add another position player to the bench on Tuesday. Deven Marrero, who was optioned on Wednesday, is not eligible to return for another six days barring an injury. The only other position players on the 40-man roster not already in the majors are Steve Selsky, Blake Swihart, and Sam Travis. Farrell said the Sox would want an infielder, so Selsky or Travis could be their choice . . . Fox Sports had the game and Don Orsillo was on the play-by-play call. Orsillo was with NESN for 15 seasons until 2015. He has been with Fox since, doing the Padres along with select national assignments. Orsillo visited the clubhouse before the game and was teased about his perpetual tan by Pedroia.