CINCINNATI -- Sammy Sosa climbed the career charts with two more homers, only to watch the Chicago Cubs let a big one slip away.

Sean Casey's homer capped a six-run sixth inning that silenced thousands of Chicago fans and rallied the Cincinnati Reds to a 9-7 victory Thursday night that left the NL Central tied up again.

Shortly after the Cubs lost, Houston beat Milwaukee 6-1 to pull into a first-place tie with three games to go. If they end up tied, their one-game playoff would be Monday at Wrigley Field.

The St. Louis Cardinals are still mathematically alive, but need to win their final three games against the Arizona Diamondbacks while Houston and Chicago both must lose their final three games.

After two days of being shut out and having their fans drowned out by thousands of Cubs supporters, the Reds put a big kink in Chicago's quest for its first division title since 1989.

The Cubs seemed to be well on their way to their overriding goal -- taking a lead and momentum back to Wrigley -- until a left-for-dead offense suddenly revived.

Sosa's two-run homer put Chicago ahead 3-0 in the third and moved him ahead of Mickey Mantle into 10th place on the career list with 537. It also gave him 100 RBIs for the ninth straight season, the first time it's been done in the National League.

By the time he rounded the bases again in the eighth on a solo homer, his 39th, the Cubs had lost their lead and their final-week momentum.

Carlos Zambrano (13-11), the youngest player on the Cubs' opening day roster, couldn't hold the early lead. Ray Olmedo's RBI single in the third broke Cincinnati's streak of 22 scoreless innings.

The Reds' offense was inept against Kerry Wood and Shawn Estes in the first two games of the series, managing only six hits. Five walks by Zambrano gave it a jump-start.

Instead of sneaking peaks at the left-field scoreboard to keep track of the Astros' game, the Cubs got engrossed in their own meltdown. The Reds sent nine batters to the plate for six runs in the sixth, their biggest inning since Sept. 9.

Casey's two-run homer off Mark Guthrie -- his first since Aug. 24 -- completed the rally, made it 8-4 and gave outnumbered Reds fans a chance to stand and be heard for the first time in the series. Casey added an RBI single in the eighth.

Todd Van Poppel (2-1) gave up four runs in five innings, then left for a pinch hitter during the comeback. Three relievers held on, with Chris Reitsma pitching the ninth for his 12th save in 18 chances despite allowing Randall Simon's home run.

Now, the Cubs' fate will be decided against another trade-stripped club, the Pittsburgh Pirates, during a three-game series at Wrigley.

The Cubs could take a little solace in Sosa's performance, an indication that their most dangerous hitter is back in form for the final weekend.

Sosa entered the series in a slump, but hit three homers in the last two games. He joined Jimmie Foxx and Rafael Palmeiro as the only players to get 35 homers and 100 RBIs nine straight years.

Sosa also became the first NL player to drive in 100 runs in nine consecutive seasons -- Willie Mays and Mel Ott reached the mark eight straight years. His 63rd multihomer game left him tied with Mays for fourth on the career list.

It's a rousing finish to one of Sosa's most disturbing seasons. He missed 17 games early in the season because of a problem with his big right toe, and served a seven-game suspension for using a corked bat.

Many of his best moments have come at the Reds' new ballpark, where he hit his 500th homer on April 4 and then homered in his return from the suspension on June 18.

Notes: Cubs manager Dusty Baker changed his pitching plans for the weekend series, deciding that 17-game winner Mark Prior will go on Friday, a day early, while Matt Clement is pushed back to Saturday. ... Mark Grudzielanek's double was the Cubs' 300th of the season. They set the club record with 340 in 1931, and have reached the mark only one other time since -- in 1935, with 303. ... Kenny Lofton was 2-for-5 with a solo homer, leaving him 11-for-25 in the last six games.