Wigginton's shot was also good news for the Astros, who avoided getting swept by the Pirates, and for starter Wandy Rodriguez, who was spared what would have been his second consecutive home loss.
Rodriguez entered Sunday's game with the third best home ERA (2.28) in the National League, and that included the seven earned runs he'd given up in his most recent home start.
The left-hander wasn't much better this time as he gave up four runs on seven hits in five innings. After allowing 15 earned runs in his first 12 home games (a 1.65 ERA), Rodriguez has been roughed up for 11 during his last two (9.58).
"I don't think he's had a lot of problems; I didn't feel like he threw his curveball over the plate today," Astros manager Phil Garner said. "His last start, I didn't think he used his changeup perhaps enough. I think what he did today was he put it to the pedal a little too hard. He was grinding. I just think he ground a little hard. He didn't pitch poorly, he kept us in the ballgame, so I wouldn't say this was a bad ballgame by any stretch."
Rodriguez agreed with that impression and said trying too hard caused him to overthrow.
"I think I wanted to throw too hard and I [went] out toward [the] third-base line with my head," Rodriguez said.
Rodriguez needed 110 pitches to get through five innings and left trailing 4-1 after giving up seven hits and three walks. He struck out seven and was saved another run when Hunter Pence ran down Adam LaRoche's drive to the gap in right-center with a fine running catch with two outs and a man on in the fifth.
The Astros crept back as Scott and Mark Loretta drove in runs in the sixth. But when the game went to the bottom of the eighth, the Astros were still trailing.
"If you're going to retire somebody's number, you can't lose the game," Astros second baseman Craig Biggio said.
With one out, Scott doubled and Shawn Chacon was brought on to face Wigginton.
Wigginton drove Chacon's first pitch into the left-field seats for his third homer since joining the Astros and 19th of the season.
"It definitely feels good any time you hit a home run to win a game," Wigginton said. "It was nice to get one today."
Wigginton's shot erased some of the offensive frustration for the Astros, who stranded five runners in scoring position. In the series, the Astros hit .194 (6-for-31) with runners in scoring position.
In the fifth, Pittsburgh second baseman Freddy Sanchez found a 3-2 fastball from Rodriguez much to his liking and promptly deposited it in the left-field seats for his 10th homer of the season and a 4-1 lead.
Rodriguez ran into some control problems in the third, and it cost him a pair of runs. He walked the bases full with one out, then gave up a two-run single to LaRoche as the Pirates took a 3-1 lead.
A two-out RBI single by Pittsburgh shortstop Cesar Izturis in the second inning had tied the game after the Astros had gone up, 1-0, in the first on Lance Berkman's single to right. Berkman's base hit scored Chris Burke, who was hit by a pitch to lead off the game before stealing second base.
Brad Lidge pitched a scoreless ninth for his 13th save. This time Lidge walked Xavier Nady, who had hit a pinch-hit home run off the right-hander Friday night to send the game to extra innings.
"He's a good hitter, he's been hitting really well against me," Lidge said. "I just wanted to be smarter with him tonight. Based on how I've been feeling, I thought I'd take my chances with the next guy."
Lidge struck out McLouth and Jose Bautista to end the game and give Bagwell his victory.
Wigginton was reminded that Bagwell began his career as a third baseman before moving across the diamond.
A little professional courtesy, from one third baseman to another?
"I don't know, I wouldn't say that," Wigginton said, chuckling. "At least I could say I was fortunate enough to get to play against him."