Haren was magnificent in beating the New York Yankees on Saturday, as he tossed a four-hit shutout and struck out seven without walking a batter to improve to 15-8 on the year, while lowering his earned run average to 3.06.
It was his third shutout of the season.
"Jeff (Mathis) called a great game and had good at-bats," said Haren, who also won 16 games for Arizona in 2008. "I was right with him from pitch one. He called an absolutely perfect game."
Haren beat the Orioles earlier in the year and is 5-2 in nine starts against them with a 3.63 ERA.
Los Angeles won for the eighth time in its last 11 games on Wednesday, as Jered Weaver picked up win No. 17 in a 4-1 win over Oakland. Mark Trumbo homered and Bobby Abreu had two hits and an RBI for the Angels, who are 3 1/2- games behind the Texas Rangers for first place in the AL West and four back of the Boston Red Sox in the wild card.
Weaver (17-7) allowed six hits and a walk to record his career-high 17th win of the year.
"It's a great thing to have," said Weaver about his new career-high in wins. "It's not over yet. We still have a lot of things to accomplish as a team."
Baltimore, meanwhile, has been relegated to the role of spoiler and made life difficult for the wild card hopeful Tampa Bay Rays this past week, taking the last two of a three game series.
On Wednesday, Chris Davis hit a three-run home run to help Baltimore win the rubber match, 6-2. Matt Wieters also homered for the third straight game, while Vladimir Guerrero added three hits and two runs scored.
Jeremy Guthrie (8-17) won his second straight start after giving up just two runs on three hits and three walks in seven innings. He also matched a career high with 10 strikeouts.
"He's been hitting his marks these past couple of spots," said Orioles manager Buck Showalter. "There's no better pitch in baseball than a well-placed fastball and he had it going tonight."
Hoping for a similar effort tonight, the O's will rely on righty Tommy Hunter, who is 3-4 with a 5.32 ERA. Hunter lost his second straight start on Sunday in Toronto, as he gave up six runs (four earned) and nine hits in 6 1/3 innings.
Hunter is a miserable 1-4 in seven games (six starts) versus the Angels with an 8.79 ERA.
The Angels have won five of their six matchups with the O's this season.