HOUSTON -- As Kevin Correia surveyed the Giants' starting infield Thursday, he was reminded of less pressurized times.

"It was almost like Spring Training," said Correia, who was backed by an all-rookie infield contingent. That didn't even count catcher Pablo Sandoval, who made his Major League debut.

"I think I probably had the same infield at one point in Spring Training," Correia continued. "But that's what we're doing right now. I have confidence in those guys, and I think they played pretty well."

Indeed, each of the five rookies contributed in varying degrees. That still wasn't enough for the Giants, however, whose bullpen continued to struggle in a 7-4 loss to the Astros that concluded a four-game series sweep for Houston -- the first one San Francisco has absorbed in Houston since Sept. 28-Oct. 1, 1970.

Interestingly, future Hall of Famers Willie Mays and Willie McCovey started every game of that season-ending series, even though it was a meaningless one. By contrast, the current Giants have less interest in their veterans and are more concerned with evaluating and developing their younger players, which is what Correia meant by "what we're doing."

The infield is so overpopulated with rookies that one of the most promising first-year players, Emmanuel Burriss, was benched after starting the previous 12 games at second base.

No judgments can be formed on the basis of one game. But although the Giants probably won't replicate the Garvey-Lopes-Russell-Cey infield quartet that helped the Dodgers thrive from the mid-1970s through the early '80s, some encouraging signs emerged.

Sandoval became the 14th Giant to make his Major League debut this season. According to the Elias Sports Bureau, that ties a franchise record established in 1926. The 22-year-old allowed a seventh-inning passed ball that helped Houston forge a 4-4 tie, but he delivered a first-inning sacrifice fly in his initial plate appearance.

First baseman Travis Ishikawa, playing his first big league game since June 2006, made a pair of slick defensive plays in the second inning and collected a double over three at-bats.

Ivan Ochoa strengthened his bid to claim the shortstop's job for 2009 by reaching as high as his 5-foot-9 frame would allow to snare Mark Loretta's seventh-inning line drive, temporarily preventing a run.

"[Loretta] didn't hit it very well, but it looked like it had enough loft to get it over [Ochoa's] head," Correia said. "It's a hard one to time, when a guy takes a big swing and he doesn't hit the barrel. He managed to jump at the right time, where he was at full stretch when he caught it."

Second baseman Eugenio Velez singled and scored twice, and third baseman Ryan Rohlinger executed an adept force play by tagging out Darin Erstad after fielding Miguel Tejada's third-inning grounder.

Yet the Giants still fell a season-high 20 games below .500 (50-70) as the bullpen ended a taxing series in which it recorded a 15.12 ERA. Every reliever allowed at least one run, including the departed Geno Espineli and excluding closer Brian Wilson, whose right arm might be calcifying due to a lack of save opportunities.

"We have to have somebody step it up here," manager Bruce Bochy said.

Fred Lewis christened the sixth inning with a Bondsian home run to right-center field to put the Giants ahead, 4-3. Correia allowed a pair of seventh-inning singles, but bequeathed that lead to Jack Taschner -- who yielded Darin Erstad's first-pitch, two-out RBI single that tied the score.

Tejada singled off Keiichi Yabu (3-5) to open Houston's eighth. In came Alex Hinshaw, who fired an 0-1 fastball that Lance Berkman redirected into the left-field seats for his 25th home run. Five of those long balls have come against the Giants, who watched Berkman hit .379 (11-for-29) with 15 RBIs against them this year. No wonder the Astros finished 7-1 against San Francisco in the season series.

Hinshaw, who retired Berkman on a harmless fly to right field Tuesday night, tried to follow a similar approach. But his pitch didn't travel far enough inside.

"When I faced him two nights ago, I got him out staying away from him," the left-hander said. "I 'showed' him fastballs in and got him out away. Today, I started away so I figured I'd show him in again. He was sitting on it and he got it. Plain and simple."