HOUSTON -- The surging Houston Astros are leaving Lance Berkman almost speechless.

Berkman hit a two-run homer in the eighth inning to help lift the Houston Astros to their eighth straight win, 7-4 over the San Francisco Giants on Thursday.

It gave Houston, which has won 16 of 20, a four-game sweep of the Giants.

"It's unexplainable," Berkman said. "This is a fairly remarkable streak. When the guys are all playing well like this, you have this feeling that you can always come back. We definitely feel like we're going to win when it's close in the seventh."

Manager Cecil Cooper says pitching has carried the Astros lately.

"That's the main thing," Cooper said. "When we've won, we've always pitched well. When you're playing like we're playing, you start to feel a little invincible."

With the score tied 4-4 in the eighth, Miguel Tejada led off with a single against reliever Keiichi Yabu (3-5). The Giants then replaced Yabu with Alex Hinshaw, who allowed Berkman's 25th home run of the year.

Hinshaw had no excuses on Berkman's homer.

"Berkman is one of the best hitters in the National League," Hinshaw said. "His numbers speak for themselves. When I got him out two nights ago, I went away from him and with fastballs in.

"Today I went away from him, but I figured I would try to go in on him again, and he was sitting on it. I just caught too much of the plate, and he hit it pretty good," he said.

Manager Bruce Bochy saw his bullpen take two of the four losses against Houston.

"It wasn't a good series for the bullpen," Bochy said. "We couldn't get anyone hot out there. That's what it comes down to. We got the lead. We did what we wanted to do out there.

"He (Hinshaw) made a mistake. He threw one right down the middle, which is not what we want him to do in that situation. The guy (Berkman) is a great hitter. He shouldn't have gotten a pitch like that, but he did," he said.

Humberto Quintero topped off the scoring with an RBI single.

LaTroy Hawkins (1-0) pitched one-third of an inning for his first win as an Astro.

Jose Valverde pitched a 1-2-3 ninth for his 30th save in 36 tries. Valverde has saves in all six appearances against the Giants this season.

Brian Moehler started and went 5 2/3 innings and allowed four runs on eight hits.

Starter Kevin Correia lasted 6 2/3 innings and allowed four runs, three earned, and seven hits and a walk. He struck out five.

Randy Winn's RBI single and a sacrifice fly by Pablo Sandoval gave the Giants a 2-0 lead in the first inning.

In the second inning, Hunter Pence doubled and went to third on a ground out. He scored on a wild pitch by Correia.

Winn's RBI double in the third made it 3-1.

The Astros tied it in the bottom of the third on an RBI double by Berkman and a sacrifice fly by Geoff Blum.

Fred Lewis' ninth homer put the Giants back on top 4-3 in the sixth. But Darin Erstad's RBI single tied it again at 4-4 in the seventh.

Notes

• Berkman's three RBI gave him 942 for his career, tying him with Jose Cruz for third on the Astros' career list.
• The Giants purchased the contract of RHP Matt Palmer from Triple-A Fresno. To make room for him on the roster, they optioned LHP Geno Espinelli to Fresno.
• Sandoval's sacrifice fly came in his first major league plate appearance in the first inning. Sandoval is the 14th Giants rookie to make his major league debut this year, a San Francisco-era club record.
• Ty Wigginton's single in the first gave him a career high-tying 11-game hitting streak.
• Aaron Rowand left the game in the second inning with a sore back. He's day to day.
• The Giants signed third-round draft pick Roger Kieschnick, the cousin of former big-leaguer Brooks Kieschnick, and fourth-round draft pick Brandon Crawford.