McGwire joined Babe Ruth as the only players to hit 50 home runs in consecutive seasons, but his St. Louis Cardinals lost to the Giants, 7-6, Wednesday on Damon Berryhill's run-scoring single in the 10th inning.
San Francisco won in the 10th after Lance Painter (0-1) walked Barry Bonds leading off. Bonds advanced to third on a pair of groundouts, J.T. Snow was intentionally walked. Berryhill, a pinch hitter, followed with a liner over the head of center fielder Ray Lankford that pull the Giants within an half-game of the Dodgers.
"That was the win of the year," said Giant Manager Dusty Baker, who used 22 players. "I was down to my last man. It's been a while for that to happen, but that's why you have a bigger roster in September."
Stan Javier's solo homer off Dennis Eckersley with one out in the bottom of the ninth sent the game into extra innings. The Giants also scored a run in the seventh and eighth as they rallied from a 6-3 deficit.
Rod Beck (5-3) pitched two scoreless innings of relief for the victory.
Meanwhile, McGwire led off the third inning with a 446-foot drive, his 16th homer since St. Louis acquired him from Oakland on July 31. McGwire, who hit a major league-leading 52 homers for the Athletics last season, became the first player with back-to-back 50-homer seasons since Ruth did it in 1927 and 1928. Ruth also accomplished the feat in 1920 and 1921.
"It's overwhelming any time you link your name with someone like that," McGwire said. "With all the ups and downs in my career, it's pretty incredible what I've done."
McGwire, back in the Bay area for the first time since the trade, also became the sixth player to reach 50 homers twice.
McGwire was not ready to start thinking seriously about Roger Maris' record of 61 homers in a season. The Cardinals have 17 games left to play.
"Let's just savor the moment now, and if it happens it happens," he said.
Bonds drove in three runs for San Francisco with a two-run homer in the first and a sacrifice fly in the third.
Montreal 5, Pittsburgh 4--Pedro Martinez (17-7) allowed three runs--two earned--and seven hits in seven innings and struck out eight at Montreal. Pittsburgh, which trails first-place Houston by 3 1/2 games in the NL Central with 16 remaining, has lost six of seven and 12 of 16.
"We came out of this road trip lucky," said Pirate Manager Gene Lamont, whose team went 1-5 on the swing. "We were 2 1/2 out when we started. We should be 6 1/2 or 7 1/2 out. We're lucky, but your luck has got to run out sometime. We've got to start winning some games."
Pirates left fielder Al Martin agreed, adding that late-season pressure may be getting to the young Pirates.
Mike Lansing and Doug Strange homered for Montreal, which completed a two-game sweep and won for the eighth time in 12 games.
Ugueth Urbina got four straight outs for his 25th save in 29 opportunities. Jon Lieber (9-14) allowed five runs and six hits in four-plus innings.
San Diego 4, Florida 3--Tony Gwynn singled home Quilvio Veras with the winning run in the bottom of the ninth inning, lifting the Padres to victory at San Diego.
Veras led off the ninth with a single to right against Ed Vosberg (1-1) and moved to second when Steve Finley was hit by a pitch. Gwynn bounced a 1-1 pitch into the hole that shortstop Edgar Renteria got a glove on but could not prevent from getting through as Veras raced home.
The hit was the 199th of the season for Gwynn, who went two for five to raise his average to .369.
Jim Bruske (4-1) worked a scoreless inning for the victory.
New York 10, Philadelphia 2--Butch Huskey and Alex Ochoa each drove in three runs as the Mets averted a three-game sweep at New York.
Ochoa had four hits and a stolen base and Huskey went three for four in extending his hitting streak to a career-high 18 games.
Brian Bohanon (5-4) allowed two runs--both unearned--and six hits in 6 1/3 innings. Matt Beech (4-9) was the loser.
Chicago 3, Cincinnati 1--Kevin Tapani (6-3) won his fourth consecutive start, allowing one run and five hits in 7 1/3 innings. Mark Grace had three hits as the Cubs won for the sixth time in eight games.
Kent Mercker (8-10) made his first start since Aug. 16, the day before he went on the disabled list because of a sore lower back. He gave up five hits over four innings.
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BESTS OF THE DAY
Player Team Performance Team's Result Barry Bonds San Francisco 2 for 3, 3 runs, 3 RBIs, HR Win Butch Huskey New York 3 for 4, 3 RBIs, 18-game hit streak Win Alex Ochoa New York 4 for 4, 3 RBIs Win Mark McGwire St. Louis 1 for 4, 2 runs, 50th home run Loss
Player Team Performance Team's Result Kevin Tapani Chicago 7 1/3 innings, 1 run, 5 hits Win Pedro Martinez Montreal 7 innings, 2 runs, 7 hits, 8 strikeouts Win