SAN FRANCISCO - Oakland Athletics rookie Mark Mulder didn't immediately realize he threw a bad pitch to Barry Bonds. The ball moved around, finally sailing directly into the path of Bonds' formidable bat.
It turned out to be the 29th homer for Bonds, who missed the All-Star game because of a slightly fractured right thumb. The San Francisco Giants went on to beat the interleague rival A's 4-2 on Thursday night.
''One bad pitch changed the game and hurt me a lot,'' Mulder (5-5) said. ''I fell behind and threw the ball down the middle. I didn't mean to, but the ball was moving a lot and came back over the plate. He's going to hit that.''
Bonds, who missed six of eight games before the All-Star break, homered in the fourth, leaving him tied with Toronto's Carlos Delgado, and one behind Mark McGwire of St. Louis and Ken Griffey Jr. of Cincinnati, who share the major league lead. It was Bonds' first homer since June 29 at Colorado.
Giants manager Dusty Baker said Bonds is clearly recovering.
''He said he was still feeling it some,'' Baker said, ''but it was a lot better than when he left (for the break).''
Russ Ortiz (5-8), just demoted from the rotation, relieved starter Joe Nathan after a scoreless, but shaky first inning and allowed one unearned run on four hits in six innings. Robb Nen pitched the ninth for his 18th save in 23 chances, allowing Eric Chavez's 14th homer.
Mulder gave up two runs and four hits in six innings.
''He gave us a chance to win,'' A's manager Art Howe said. ''He made one mistake to Bonds. He got behind him 2-0 and that's not a good situation to be in.''
Pinch-hitter Marvin Benard extended the lead to 4-1 in the seventh with a two-run single off Doug Jones. San Francisco loaded the bases when Ellis Burks tripled, Bill Mueller walked and J.T. Snow reached on third baseman Chavez's error.
Snow's RBI single put San Francisco ahead in the second, but Jason Giambi's sacrifice fly tied the score in the third.
Nathan loaded the bases in the first inning on Terrence Long's single and one-out walks to Giambi and Ben Grieve. Miguel Tejada and Matt Stairs then popped out.
Nathan, who was on the disabled list earlier this season with tendinitis in his right shoulder, felt tightness in the shoulder while warming up and during his short appearance.
''I wasn't sure if he wasn't getting loose, but I knew he wasn't getting extended like he usually does,'' Giants catcher Bobby Estalella said. ''He threw some good pitches, then he was a little wild.''
Team trainer Stan Conte said Nathan was set to have an MRI on Friday.
''The best case scenario is that it's tendinitis, and we'll treat it as such,'' Conte said. ''He'll possibly miss a start, but I'm not wiping that out.''
Ortiz was 4-8 with a 6.92 ERA before he was sent to the bullpen, winning once - at Houston on June 25 - in his last nine starts.
Ortiz didn't let on that he was thrown off by the demotion.
''I told them I'd be ready whenever they needed me, both mentally and physically,'' he said.
Notes:
Ortiz's previous relief appearance was at Chicago on Sept. 28, 1998. ... The Athletics placed DH John Jaha on the 15-day disabled list with tendinitis in his left shoulder. It's possible Jaha will have surgery, which will keep him out for six weeks. The A's recalled Adam Piatt from Triple-A Sacramento to fill the roster spot. Piatt, who joins the A's for the third time this season, hit .283 with eight home runs in 65 games with Sacramento. ... The Giants will continue their charity Until There's a Cure Day at their new digs, Pacific Bell Park. The event, which raises money for AIDS research and treatment, will be held July 16 when the Giants play the Rangers. The Giants were one of the first teams to raise money for the cause.