"It was fun seeing him out there," Haren said. "I had a few flashbacks from Pepperdine."
Mark Kotsay added an RBI double, and Eric Chavez drove in a run for the A's, who won for the seventh time in eight games. They have clinched a winning record for June -- their first winning month since going 20-8 last August.
Haren (6-7) won his fifth straight decision, pitching a seven-hitter for his second career complete game. Haren, who struck out five and didn't walk a batter for the fourth time this year, threw a five-hitter against Tampa Bay on May 31.
His gem came a day after rookie Joe Blanton won his third straight start.
"We're all pitching with confidence, even a chip on our shoulder like we're better than the other guy," Haren said. "I'm going out there thinking that I'm going to beat him, as opposed to early in the year when I was scared a little or worried I was going to lose."
Moises Alou homered, doubled and singled as designated hitter, and Mike Matheny also homered for the Giants, who made five errors and lost for the 21st time in 28 games. It was the most errors for San Francisco since it had six at Montreal on April 29, 1999.
"The sun's been there for a billion years," manager Felipe Alou said, refusing to use that as an excuse. "I feel sick today about the game."
All three of his outfielders made errors, something Alou hadn't seen since managing Class-A ball in Florida. The Giants hadn't done that since at least 1980.
Lowry (4-7) allowed five runs -- four earned -- five hits and four walks in six innings. He and Haren were teammates at Pepperdine for two seasons, live in the same condominium complex in San Francisco and even rode to Friday's game together. Haren's place is directly above Lowry's. They've been to dinner together several times.
"We can go back to being friends again," Lowry said.
Haren, acquired from St. Louis in the December trade that sent Mark Mulder to the Cardinals, was winless in seven starts before his recent hot stretch. He retired his first seven batters before Matheny's solo homer in the third and 18 of his first 21. Haren allowed three hits in the seventh, including an RBI double by Todd Linden.
The shaggy-haired right-hander is fitting in well with this laid-back team and a rotation led by the zany Barry Zito.
Lowry struck out the side in the first after Jason Kendall's leadoff walk. But the lefty, in his first full major-league season, got into trouble in the second. Bobby Kielty singled and, two batters later, Dan Johnson walked. Swisher then connected for his sixth homer.
"As a pitcher, you can only control so much in the game," Lowry said. "I tried to minimize the damage. ... We don't make a ton of errors. Today was just a bad day."
Alex Sanchez, claimed off waivers from Tampa Bay on Thursday, started in right field and hit leadoff in his first appearance with the Giants. Sanchez was involved in two of San Francisco's errors, dropping a fly ball by Eric Byrnes in the eighth, then colliding with center fielder Jason Ellison moments later. Ellison was charged with the error that allowed Johnson to reach.
"Sanchez is usually a center fielder and the center fielder has priority," Alou said. "The ball was there for several minutes. Someone has to make the call. We've been playing pretty well defensively. It's unusual to see this. My guys played really bad today."
Ellison said that Sanchez had trouble hearing him on the play.
Sanchez, known for his bunting talent and defensive blunders, did have a sacrifice bunt in the sixth. Despite his mistakes, Alou was leaning toward playing him again Sunday, perhaps as the designated hitter.
"I'm not going to put up excuses," Sanchez said. "Everyone saw me call the ball. He's coming from center field. I'm trying to make the play, and he drops it."
Byrnes had a nice catch of a hard-hit foul by Ray Durham in the seventh, slamming into the wall to make the grab. He also had a diving catch in the sixth before making a baserunning mistake in the eighth.
"It felt like I ran into a Mack Truck," Byrnes said. "I think every morning I wake up I'm a little dazed. For some reason, I'm used to hitting things with my head."
"He's worth the price of admission," Swisher said.
- Barry Bonds won't travel with the Giants on their trip to Arizona and San Diego, staying in San Francisco to do rehab on his surgically repaired right knee.
- The game drew a sellout crowd of 46,763.
- Kendall had his eight-game hitting streak snapped.
- Durham returned after missing Friday's 4-3 loss with a lower back strain.