"They were fighting to get back in it," manager Bruce Bochy said of his club. "You have to put the really good games, just like the tough ones, behind you."
Giants starters hadn't given up a walk to the Astros in the series entering Thursday's game, but Zito walked three consecutive batters in the third to load the bases for Martinez, who made the veteran lefty pay by sending a ball to the left-field seats.
"You saw him. He was making some mistakes and falling behind and walking guys, and I was going up there aggressive because I knew he had to give me something to hit," Martinez said. "He wasn't going to fall too far behind and he had to give me something. That's the kind of mindset I went up there with, was be aggressive."
"Walks killed us," Bochy said, noting that four of the Astros who scored reached base on walks. "We had trouble getting the ball over the plate. Those things are going to beat you."
Zito pitched five innings, getting tagged with a season-high five runs on five hits and three walks.
"I felt like I was locating decently, but that one inning, things got away [from me]," Zito said.
The 13-year veteran said he shrugged off any pressure of following Cain's perfect game, which ended less than 15 hours before Thursday's game.
"You can't do that. You have to just go out there and make your pitches," Zito said. "That's what Matty did yesterday, and then things happen from there out of your control."
Brandon Belt started a Giants rally by homering in his third consecutive game after having gone the entire season without a home run. He hit a two-run blast to McCovey Cove in the fourth for the Giants' 61st Splash Hit and the first by a Giant this season. His last home run before the Astros series had come against the Rockies on Sept. 27.
"He's starting to find his swing, against lefties, too, which is good to see," Bochy said. "He made a couple good adjustments out there. That's a good sign for us and a good sign for him."
Astros starter Wandy Rodriguez gave up three runs in six innings for the Astros, and the Houston bullpen held the Giants scoreless in three innings of work.
"Their guy pitched pretty good," Bochy said. "We had him on the ropes early, but he pitched out of it."
The Giants cut the Astros' lead to two runs when Angel Pagan scored on Hector Sanchez's sacrifice fly in the sixth, but the Astros picked up another insurance run when Justin Maxwell singled home Brian Bixler in the eighth. San Francisco fell to 1-26 when trailing after seven innings.
"If we would have come out here and won to get the sweep, that would have been great," Belt said, adding that he was still feeling the lingering effects from the last night's historic win. "It doesn't always work like that. That's part of baseball.
"It was hard to get any sleep, and I think it was the same for everybody. It might have played into today, but we'll get them tomorrow."