Erstad's pinch-hit solo homer lifted Houston to a 5-4 win over the Atlanta Braves, but the Astros were eliminated from the NL wild-card race when Milwaukee beat Chicago.
Michael Bourn also scored from second on a third-inning sacrifice fly for Houston, which entered 3 1/2 games back of the New York Mets and Milwaukee for the wild card. The Astros celebrated Erstad's shot at home plate, then returned to their clubhouse just in time to watch the Brewers finish a 5-1 victory at Miller Park.
"It's obviously bittersweet to go from winning to, literally three minutes later, watching Milwaukee pull this out," Erstad said. "We didn't hand it to them. They had to win. This team kept fighting."
Erstad's third career game-winning homer bailed out closer Jose Valverde (6-3), who gave up the tying run in the top of the ninth. Julian Tavarez (1-4) retired Humberto Quintero in the bottom half and Erstad homered to right on the next pitch.
The Astros are 41-23 since the All-Star break, second only to the Angels in the majors. They're 21-10 since Aug. 23, despite a five-game losing streak in the wake of Hurricane Ike.
"We could've mailed it in about a month and a half ago," manager Cecil Cooper said. "They continued to play and we got contributions from all over the board. That says a lot about the team we have."
The hurricane hit Houston on Sept. 12 and forced the Astros to play two scheduled home games against the Cubs in Milwaukee. Playing in front of mostly Cubs fans, Houston lost both games -- getting no-hit by Carlos Zambrano in the opener.
The third game of the series was postponed and would've been played in Houston on Monday if it had playoff implications.
"We ran out of games. That's what it came down to," starter Brian Moehler said. "But we played well the last few months. We battled and we made it interesting when people thought we were out of it."
Houston led 4-0 after three innings against Jorge Campillo.
Kaz Matsui led off the first with a double to right. Bourn bunted and Campillo fielded it, but his throw bounced away from first baseman Casey Kotchman and Matsui scored. Campillo was charged with an error.
"I thought I had it," Francoeur said. "It would have been a tough play. My arm went all the way back. The fan caught it above me. It's not like he reached over the stands."
Bourn beat out an infield hit in the third and advanced on Miguel Tejada's groundout. Lance Berkman flew out to deep center and the speedy Bourn raced home to push the lead to 3-0. Hunter Pence added an RBI double.
Kotchman hit a two-run single off Moehler after the Braves loaded the bases in the fourth.
Buddy Carlyle relieved Campillo for the Houston fourth. Campillo threw 51 pitches, giving up seven hits.
The 30-year-old Campillo was making his 25th start and manager Bobby Cox thought he looked tired.
"He was just pitched out," Cox said. "I thought about not starting him. He had a great season. I told him that when I took him out."
Cooper brought in left-hander Tim Byrdak to replace Moehler with two outs in the sixth. Moehler allowed only four hits.
Kelly Johnson's sacrifice fly off LaTroy Hawkins in the eighth cut Houston's lead to 4-3. It was the first run allowed by Hawkins in 23 appearances since the Astros acquired him from the New York Yankees on July 30.
Valverde relieved to start the ninth and gave up a leadoff walk to Omar Infante and a single to Francoeur.
Brandon Jones then hit a grounder to Berkman at first and he threw to Tejada to start a double play. Valverde mishandled the relay throw and Infante scored to tie it at 4.
Valverde blew his seventh save chance. He had converted 27 of his previous 29.
"The big boy has been terrific," Cooper said. "He was probably due for one."
Atlanta slugger Chipper Jones was out of the starting lineup for the sixth straight game with soreness in his right shoulder. ... Mike Hampton (3-3) will start Sunday's finale for Atlanta, replacing Jair Jurrjens (13-10). ... Johnson went 0-for-2, ending a 22-game hitting streak. It had been the longest active streak in the majors.