The Athletics traded for Scott Sizemore because they needed help at third base and he has a nice on-base percentage. Any power hitting was purely a bonus.
"I'm not going to hit a lot of home runs but it's nice to hit one," Sizemore said. "He left a change up and I saw it well out of his hand and hit it pretty well."
Jackson and Sizemore connected in the sixth, the first time the A's have hit two home runs in an inning all season. It was Sizemore's second homer this year.
"He's a good on-base guy and hits the ball the other way," A's manager Bob Melvin said. "He's gained a lot of confidence and has become an everyday third baseman. He's been a productive player."
Xavier Nady and Sean Burroughs drove in runs for the Diamondbacks, who lost their third consecutive series and have lost four of their last five games.
"We had a lot of chances but we were unable to take advantage," Diamondbacks manager Kirk Gibson said. "Gio is pretty good and you have to give him credit. He knows how to pitch. He has electric stuff."
Gonzalez (8-5) allowed a run and walked three in seven innings. He is 3-0 with a 1.29 ERA over his last four starts.
Earlier in the day, the AL All-Star roster was announced and he was included.
"I didn't want to get over excited," Gonzalez said. "It's always been a secret goal for myself. I just want to enjoy the moment and move forward to get myself ready for my next start."
Gonzalez is now third in the AL with a 2.31 ERA after throwing a career-high 119 pitches.
"There was a lot more going through his head," Melvin said. "You want him to focus and not have any more distractions. He's a fun-loving kid who likes to smell the roses. His leadership comes when he takes the ball because we feel we have a good chance to win with him."
Ian Kennedy (8-3) lasted 5 2-3 innings, giving up seven runs on a season-high 10 hits. He walked two and struck out six.
"The command wasn't the same," Kennedy said. "I wasn't executing the same as I was in the first couple innings. It was me not throwing enough strikes."
Kennedy lost for the second time since April 13 and for the first time on the road. He extended his streak of consecutive games with at least 100 pitches to 15, matching the longest active streak in the NL with Philadelphia's Roy Halladay.
The Diamondbacks took a 1-0 lead in the fourth. Chris Young doubled to open the inning and Nady singled him home two outs later.
The A's responded in their half of the fourth. Coco Crisp, who has an eight-game hitting streak, and Hideki Matsui led off with singles. Two outs later, DeJesus delivered a two-run double, his first RBIs since May 31, a span of 23 games.
Joey Devine relieved Wuertz and got the next two hitters before Burroughs' pinch-hit single drove in Upton. Matsui's throw from left field got Young, who did not slide, at the plate. It was Matsui's first outfield assist since May 23, 2008, against Seattle.
NOTES: A's RHP Brandon McCarthy was activated from the 15-day disabled list and will start Monday. The A's optioned LHP Josh Outman to Triple-A Sacramento to make room. "It was not performance-based," A's manager Bob Melvin said. "It was a numbers thing." ... Upton has Gibson's blessing if he wants to participate in the All-Star home run derby. "If he wants to do it and he's asked, I have no problem with it," Gibson said. ... Gametime temperature was 83 degrees, the season's hottest day in Oakland. ... A's OF Josh Willingham (strained left Achilles' tendon) had a setback following two rehab games and is day-to-day. "It stiffened up on him," Melvin said. ... Oakland RHPs Grant Balfour (strained right oblique) and Tyson Ross (strained left oblique) threw off the bullpen mound before the game.