Pineiro gets the ball for the Angels on Monday when they open a two-game set in Oakland.
A sore shoulder caused Pineiro (2-0, 1.33 ERA) to miss the first month of the season, debuting against Tampa Bay on April 30. He's looked fully healthy since his return, giving up three runs and 15 hits in his first 20 1-3 innings.
The right-hander allowed two runs in 7 2-3 innings of a 6-2 win over the Chicago White Sox on Tuesday.
"Joel mixed up his pitches, changed speeds, pitched well," manager Mike Scioscia said. "He really has four pitches he can use, and when he mixed them up, he can be effective."
Pineiro went 1-0 with a 1.57 ERA in three starts against the Athletics (20-20) last year. The Angels (22-19) won all three.
Los Angeles dropped two of three at Texas over the weekend, closing the set with a 5-4 loss Sunday. The Angels stranded 11 baserunners, finishing the weekend 3 for 31 with men in scoring position.
"We didn't do enough," Scioscia said. "We have to pick up the pieces of that game. ... It's no barometer of things to come. We know what we need to clean up and do better."
The Los Angeles bullpen has also been shaky, blowing three saves in five chances and posting a 7.36 ERA over the last seven games.
Timely hitting has been a problem all season for the Athletics, who have scored three runs or fewer in eight of their last 11. They lost two of three to Chicago over the weekend, including a 4-3 defeat Sunday.
Trevor Cahill suffered his first loss of the season and Oakland stranded 10 on base.
"The big hit, when we needed it, eluded us,'' manager Bob Geren said.
Coco Crisp is batting .167 in his last 10 games, but had three hits in the final two games of the weekend series, including a home run Sunday.
On Monday, the Athletics will hand the ball to Brett Anderson (2-3, 3.21), who will take his fifth crack at defeating the Angels. The left-hander is 0-2 with a 4.68 ERA in four career starts versus Los Angeles.
Anderson surrendered four runs, six hits and four walks in 4 2-3 innings of a 7-2 loss to Texas on Tuesday. It was the second time in three starts Anderson gave up at least four runs - both against the Rangers. He has a 1.65 ERA in his other six starts.
Erick Aybar, who is 0 for 7 against Anderson, is looking to extend a 13-game hitting streak during which he's batting .373. He went 3 for 11 in last month's series versus the A's.
The Angels won two of three in that set but dropped six of 10 in Oakland last season, scoring two runs or fewer six times.