The Mets, 15-4 since the break, moved a game in front of the Atlanta Braves, who lost to Pittsburgh 7-1. The Brewers lost their fourth straight game and have dropped nine of 11.
Ventura, who has six homers and 12 RBIs in his last seven games, had RBI singles in the first and third innings and hit his team-high 24th homer for a 6-2 lead in the fifth. He walked in the seventh and added a single in the eighth.
"Over the course of my career, I've been streaky in that way," Ventura said. "Where, for a long period of time I won't hit a lot of home runs, and then I'll go for a while where I hit them. Usually more in the second half than the first half and I don't know why."
Piazza had an RBI groundout in the first and his 23rd home run in the eighth.
Hershiser allowed six hits, struck out four and walked two. Turk Wendell got a double-play grounder in the eighth and Masato Yoshii, demoted to the bullpen with the arrival of Kenny Rogers from Oakland, retired the side on four pitches in the ninth.
It was Yoshii's first relief appearance after 49 starts for the Mets.
Bill Pulsipher (3-2) allowed six runs four earned and nine hits in five innings in his first start against his former team.
"They've got a heck of a ballclub," Pulsipher said. "It's tough to see (Edgardo) Alfonzo, (John) Olerud, Piazza and Ventura right in a row there. It's a pretty tough lineup."
The Mets scored twice in the first after loading the bases with no outs. Roger Cedeno and Alfonzo opened with consecutive singles and Olerud was hit by a pitch.
Piazza bounced to first baseman Mark Loretta who threw to second for the force, allowing Cedeno to score. Piazza was safe when Pulsipher failed to cover first on the relay. Ventura followed with a run-scoring single to make it 2-0.
Ventura's RBI single in the third made it 3-0, but the Brewers answered in the bottom of the inning. Brian Banks led off with his fourth homer, snapping an 0-for-15 skid, and Jeff Cirillo added a two-out RBI single to make it 3-2.
New York increased the lead to 5-2 in the fourth on a two-run throwing error by the catcher Banks. Shawon Dunston and Rey Ordonez opened with consecutive singles. After Hershiser struck out, Dunston and Ordonez attempted a double steal on a third strike pitch to Cedeno. Banks threw wildly down the third-base line, allowing both runners to score.
The Mets added a run in the seventh on Dunston's RBI single.
Brewers manager Phil Garner said the Mets are much deeper than just Piazza and Ventura.
"That's not all their ballclub," Garner said. "Their shortstop (Ordonez) is a big part of their ballclub. I think the second baseman (Alfonzo) is a terrific player. He may be their best all-around player. Ventura's a pretty good all-around player. Olerud is a pretty good player. They've got a nice thing going right now. They're all playing very well."
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