HOUSTON — Nothing could pull Barry Zito out of his rhythm Tuesday night. Not six minutes for an instant-replay review. Not six months between starts.

For the first time in a long time, Zito began a season with positive vibes. He handled a depleted Houston Astros lineup over six innings, and four relievers finished out the Giants' 3-0 victory at Minute Maid Park.

Zito hadn't opened the season with a win since 2003 with the Oakland A's, when he was the defending AL Cy Young Award winner. He had been 0-6 with a 7.06 ERA in six previous season debuts.

Generally, Zito doesn't dwell on such minutiae. But he acknowledged the personal significance of the win.

"Yeah, definitely," said Zito, who struck out five and walked one. "You want to let the team know I'm going to carry my load here. I'm one of five."

Two nights into the season, the Giants already own a series victory.

As in Monday's opening-night win over Roy Oswalt, their offense put together one well choreographed inning, and their pitching did the rest.

A three-run rally against Wandy Rodriguez in the sixth began when Edgar Renteria and Pablo Sandoval drew walks — no small detail for a team that drew the fewest bases on balls in the majors last season.

Aubrey Huff and Juan Uribe hit run-scoring singles, and Sandoval turned contortionist while avoiding catcher Humberto Quintero's tag on Bengie Molina's sacrifice fly.

But nothing was more encouraging than Zito, who never broke focus as he established his fastball and mixed sequences. He threw first-pitch strikes to 11 of the first 15 batters.

"Epic performance," said closer Brian Wilson, who registered his second save. "One pitch that was on fire today was his slider. He'd been working on that last year. Today, it was on cue."

At what point this spring could manager Bruce Bochy foresee this kind of outing from Zito?

"Really, I'll start with how he threw the ball last year," Bochy said. "He took that into spring training. He came in with a different look. He had one little hiccup there, but he knew he was getting a little quick. He fixed it.

"He had a good groove and stayed in it."

Zito easily could have lost focus in the sixth after Jeff Keppinger hit a deep drive off the top of the left-field wall. Umpires called it a double and walked down the tunnel to review video, which upheld the ruling.

"A lot of the guys were socializing there to kill time, but I wanted to stay on the mound and throw pitches," Zito said. "I just had to stay in the zone."

The Astros are without disabled first baseman Lance Berkman, and they probably won't light up the scoreboard this season. But Hunter Pence and Carlos Lee are dangerous hitters, and Zito had to face them after the delay.

Pence flied out and Lee popped up a well-placed fastball.

"He stayed locked in," Bochy said.

Also uninterrupted is the mojo from a solid spring in which the Giants led all major league clubs with 23 victories.

"It wasn't by accident," Wilson said. "We've been winning a lot of these games the same way. The pitching held their own, we put up a crooked number, and then we preserved it."

One player who hasn't carried over his spring success is leadoff man Aaron Rowand, who hit better than .400 in exhibition games but is 0-for-10 and hasn't been on base in two games.

Bochy said he has no plans to sit Rowand.

"It's two games, and you know, it happens," Bochy said. "He just needs a hit to get going."

As Zito can attest, that first one does wonders.