PITTSBURGH -- The home run was very important. The run home by Jason Bay was better still.

Bay became the first Pirates player in 50 years to homer in five consecutive games, then ran over Houston catcher Eric Munson to score the winning run on Jose Bautista's short sacrifice fly in the 18th inning as Pittsburgh beat the Astros 8-7 Saturday night.

The game was the longest in Pittsburgh since PNC Park opened in 2001 and the Pirates' longest at home since a 4-3, 18-inning win over the Cubs on Aug. 6, 1989. The Astros beat Atlanta last year in an 18-inning NL playoff game, the longest postseason game in history, but hadn't played a regular season game so long since a 22-inning win over the Dodgers on June 3, 1989.

"At some point, you don't even know what inning it is," Bay said.

The Astros lost their fifth in a row and have dropped 16 of 22 since starting the season 19-9.

Houston took a 7-6 lead on Willy Taveras' two-out single up the middle in the 17th against Ryan Vogelsong -- the first run since Jeromy Burnitz's pinch-hit homer for Pittsburgh tied it at six in the eighth. But Jose Castillo greeted Mike Gallo, Houston's sixth reliever, with his second homer in as many games to lead off the bottom of the inning. Castillo's fourth homer of the season ended a streak of eight shutout innings by Astros relievers.

Gallo (1-1) walked Bay to start the 18th, then threw two wild pitches -- one while intentionally walking Craig Wilson -- to advance Bay to third. Bay then chose to go home on the short fly ball and was safe when Munson couldn't hold the throw from Taveras.

"I just lowered my shoulder and flew over top of him," Bay said. "I don't know what happened. I was just trying to score."

Gallo took responsibility for the loss, saying of the wild pitch to Wilson: "It's one that got away, and I'm embarrassed about it because I'm a professional athlete and that stuff, that's just knowing your ABCs, and you're not supposed to do that. I let my team down. And it magnifies everything because of the way our road trip is going."

Victor Santos (2-5), the ninth Pirates pitcher and their scheduled starter Monday against Milwaukee, pitched a scoreless 18th for the victory.

Bay is the first Pirates player to homer in five consecutive games since Dale Long became the first in major league history to homer in eight in a row, in 1956. Bay hit the first pitch he saw from Astros starter Wandy Rodriguez in the fifth for a three-run drive that put the Pirates up 5-4, his 15th of the season.

"That seems like three days ago," Bay said. "Like I've said, when you're going well you try to ride it as long as you can."

Bay's ninth homer in 35 at-bats over nine games -- a span that includes two two-homer games -- followed his RBI single in a two-run Pirates first and gave him four RBI for the second night in a row. That Pirates first was helped by two Astros infield errors, by first baseman Mike Lamb on Nate McLouth's easy grounder to start the game and shortstop Adam Everett's two-base throwing error on Bautista's grounder that also scored a run.

Bay also figured in what briefly proved to be the Astros' go-ahead run in the eighth. After reliever Roberto Hernandez walked two and hit a batter to load the bases, Lamb's fly ball to the warning track fell out of Bay's glove for an error as he stumbled backward. Bay recovered to make a strong relay throw to shortstop Jack Wilson, who threw Burke out at the plate on a disputed call that led to manager Phil Garner's ejection.

Because Lamb's drive was long enough to score Biggio even if Bay had caught the ball, the error became meaningless when Burke was thrown out.

Pirates reliever Mike Gonzalez felt the key to the game was Vogelsong, the mopup man in the Pirates' bullpen, limiting the Astros to a run over five innings.

"That was huge. He saved the starting rotation, definitely," Gonzalez said. "Sometimes he'll sit down there seven, 10 days without pitching, and we all feel for him and want him to be successful."

Pirates starter Paul Maholm, who had allowed only eight earned runs in his previous five starts, took a 2-0 lead into the fifth only to have the Astros score four times.

"We'll be tested now, we have to bounce back from this, but that's what you're supposed to do," Garner said.

Notes

• The Pirates had not played a home game longer than 15 innings since PNC Park opened
• Kevin Mench of the Rangers homered in a major-league season high seven games in a row earlier this season, and Ensberg homered in six in a row.
• Pirates RHP Salomon Torres pitched for the seventh time in eight games, retiring all three batters he faced in the seventh. He has pitched in 12 games in 17 days.
• The Pirates are 2-15 when an opponent starts a left-hander.
• Craig Biggio's single in the sixth was his 2,848th hit, tying him with Brooks Robinson for 40th place in major league history.
• Bay has 10 homers and 32 RBI in his last 18 games.
• Astros 1B Lance Berkman, lifted in the third inning Thursday in Washington with a hyperextended knee, walked as a pinch-hitter in the eighth.
• Pirates 1B Sean Casey (back) went 1-for-3 with a solo homer on a rehabilitation assignment at Double-A Altoona.
• Burnitz is 10-for-20 in his last six games.
• The Pirates left the bases loaded in the 11th when Chad Qualls got Bautista to ground into a force play. Before his sacrifice fly, Bautista had not hit the ball out of the infield in six at-bats.