OAKLAND, Calif. (AP) -- Jeremy Giambi was upset at himself for not getting a bunt down. Just a few seconds later, he was celebrating his game-winning hit.

Giambi's RBI single in the bottom of the 10th inning gave the Oakland Athletics an 8-7 victory over the Arizona Diamondbacks on Saturday night in front of the largest baseball crowd in Oakland Coliseum history and gave him a career-high five RBI.

In front of 54,268, Greg Swindell (1-2) walked Ben Grieve and John Jaha to open the inning. Ryan Christenson, who came in to pinch-run for Grieve, scored the game-winning run on Giambi's single to right field.

"I was frustrated I wasn't able to bunt," Giambi said. "Then I decided to try and bunt on my own with two strikes, but I took the pitch. Then Swindell threw me a fastball and I found a hole."

Jason Isringhausen (4-2) pitched a scoreless inning to pick up the victory.

"Jeremy can handle the bat pretty well," A's manager Art Howe said. "They have one of the best bullpens in the game, but we were able to cash in."

Giambi hit a grand slam off Arizona relief pitcher Dan Plesac, then Miguel Tejada followed with a solo shot, his second of the game, off Diamondbacks closer Byung-Hyun Kim to tie it at 7 in the eighth. It was Kim's third blown save of the year.

"I don't know if he sees the ball well against me or not, but it was like he knew it was coming," Plesac said.

With one out and the Diamondbacks leading 7-2, both Olmedo Saenz and Grieve singled and Arizona's Vicente Padilla walked John Jaha to load the bases. Plesac then entered the game and Giambi hit his 3-2 pitch over the center-field fence. Kim replaced Plesac, and Tejada hit a 2-1 pitch into the left-field bleachers to tie it.

"Early in the count, I was thinking fastball," Giambi said. "But he kept throwing me sliders. With the full count, I still thought fastball. That's the best ball I've hit in my career. I got all of that one."

The Diamondbacks scored four runs in the eighth to take a 7-2 lead.

Steve Finley, Travis Lee and Danny Bautista drove in runs in the inning, and Craig Counsell scored on a wild pitch.

A's starter Kevin Appier was perfect through five innings, but had trouble getting out of the sixth.

Gonzalez doubled home two runs and Counsell hit an RBI double to give Arizona a 3-1 lead.

Diamondbacks starter Brian Anderson allowed two runs on seven hits, struck out three and walked two in 6 2/3 innings. Anderson has allowed five earned runs in his last 28 2/3 innings for a 1.57 ERA.

"One of our strengths has been the bullpen and we've had a couple of tough nights here," Arizona manager Buck Showalter said. "You just have to tip your hat to them."

Appier retired the first 15 batters in order before allowing a leadoff triple to Rob Ryan in the sixth. He gave up five runs on five hits in seven innings, striking out four and walking two.

Randy Velarde gave the A's a 1-0 lead in the first with his seventh homer.

Tejada's 14th homer came with one out in the seventh to get Oakland within 3-2.

Game notes
Arizona 3B Danny Klassen, who left Friday night's game with turf toe, was not in the starting lineup Saturday, though Showalter said he would be available for pinch-hitting duties. ... The A's have hit eight grand slams this season, tying a franchise record (1932 and `99). ... Arizona 3B Matt Williams, on the DL with a strained right quad, began a rehab assignment with Class-A High Desert of the California League. ... 1B Erubiel Durazo, on the DL recovering from right wrist surgery, also begin his rehab assignment on Saturday. Durazo was to play at Triple-A Tucson of the PCL. ... The A's signed LHP Mike Mohler to a minor league contract and sent him to Triple-A Sacramento of the PCL. Mohler started his career with Oakland in 1993. ... A's 3B Eric Chavez, who snapped an 0-for-20 streak Friday night, was not in Saturday's lineup against Anderson. Chavez is also not expected to start Sunday against Randy Johnson. ... The A's are 6-1 in extra-inning games this year.