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HOUSTON -- Joe Martinez handled his nerves, with considerable help from batterymate Eli Whiteside.

Martinez came off the disabled list to win his first major league start, Whiteside hit a grand slam for his first career home run and the San Francisco Giants rallied for a 10-6 win over the Houston Astros on Wednesday.

Martinez (2-0) pitched in the majors for the first time since he was struck in the head by a line drive from Milwaukee's Mike Cameron on April 9.

Martinez said he was nervous before the game, but only because he missed the last four months. He was injured in his second relief appearance of the season.

"That's kind of hard, being a starter, you have to deal with the buildup," he said. "In ways, it's good, because you always know when you're going to pitch. In other ways, it's tough because you anticipate it so much, you get yourself a little too worked up."

The 26-year-old rookie made seven starts in the minors before he was reinstated from the 60-day disabled list to start against Houston. He gave up three runs and seven hits in five innings.

"I was a little jumpy at the beginning," he said. "After I settled down, I felt great. To get a win is even better."

Whiteside started in place of Bengie Molina, who had the day off to rest. Early in the game, Whiteside told Martinez he was hurrying his pitching motion, and the right-hander allowed only two hits over his last three innings.

"After that second inning, he got that thing fixed and pitched well," Whiteside said.

Whiteside's slam gave the Giants a 7-3 lead in the sixth against Brian Moehler (7-7), who dropped to 0-2 with a 6.75 ERA in his last three starts. He nonchalantly flipped the bat and started an easy trot the moment he hit it, already knowing where the ball was headed.

"It was nice, for one, to put the barrel on the ball," said Whiteside, who came in with a .224 average. "It just felt good. I've been a little frustrated at the plate, I haven't been doing anything productive. That was a little frustration coming out."

The Astros have lost nine of 12.

"Definitely a disappointing day," Houston manager Cecil Cooper said. "We could have used a gritty seven innings, but we didn't get it. I thought Moehler threw the ball OK early in the ballgame but in the sixth couldn't make a pitch."

Jason Michaels helped the Astros get off to a fast start. Michaels, who got the start in center with Michael Bourn resting a sore groin, hit a two-run double and scored on Kaz Matsui's two-out single to make it 3-0 in the first inning.

Pablo Sandoval singled in a pair of runs in the third for the Giants and sparked San Francisco's rally in the sixth. He singled with one out, went to second on a wild pitch and scored on Ryan Garko's single to left.

Aaron Rowand followed with a double to the left-field corner and Moehler intentionally walked Edgar Renteria to load the bases for Whiteside, who hammered the right-hander's first pitch high over the left-field wall for the Giants' third slam of the season.

"That's one I know he'll always remember -- tie ballgame, bases loaded," Giants manager Bruce Bochy said. "It won the game for us."

Garko added a run-scoring triple in the seventh against Chris Sampson and the Giants tacked on two more runs in the ninth against Alberto Arias.

Hunter Pence hit a two-run homer in the ninth for Houston.

The Giants won for the 10th time in 14 games and rallied from three runs down to win for the first time this season.

Game notes

Astros right-hander Roy Oswalt threw about 40 to 50 pitches off flat ground and is scheduled to throw a bullpen session on Friday. Oswalt left his last start with an irritated disk and said he was still feeling discomfort after a bullpen session on Monday. General manager Ed Wade hopes Oswalt will be ready to start Tuesday's game in Florida. ... Astros left-hander Wandy Rodriguez threw a bullpen session and Wade was hopeful that he could start Sunday's game against Milwaukee. ... The Giants optioned right-hander Waldis Joaquin to Triple-A Fresno. The 22-year-old Joaquin made his major league debut on Tuesday night, allowing a run and two hits in the ninth inning of the Giants' 8-1 win. The Giants also placed right-hander Henry Sosa on the 60-day disabled list with a torn shoulder muscle.