The Cardinals took two of three from NL Central-leading Milwaukee and pulled within one game of the division lead.
Lackey (1-0) was the Cardinals' big catch at the trade deadline that capitalized on Boston's sell-off. The right-hander won the clinching Game 6 of the World Series against St. Louis last fall allowed two runs and seven hits in seven innings and is 12-7 overall.
Trevor Rosenthal struck out Carlos Gomez with two on for his major league-leading 34th save in 38 chances.
Milwaukee starter Matt Garza was pulled after allowing one hit in six innings.
Matt Holliday homered off Zach Duke with one out in the seventh. Recently acquired A.J. Pierzynski hit a tying single off Jeremy Jeffress (0-1) and Taveras singled up the middle.
Aramis Ramirez had an RBI single in the first for Milwaukee, his seventh hit of the series, and Mark Reynolds hit his 19th homer in the second.
Manager Ron Roenicke opted for pinch-hitter Lyle Overbay to bat for Garza in the seventh with two outs, a runner on first and the Brewers up 2-0.
Overbay singled, raising his career average to .364 against Lackey, but Gomez popped up. Garza was out after just 71 pitches, and the Brewers' bullpen quickly surrendered the lead.
Garza needed just 38 pitches and faced the minimum the first four innings. He went to a full count for the first time against Matt Adams, who doubled leading off the fifth.
Brewers: Second baseman Scooter Gennett and shortstop Jean Segura did not start, both nursing sore quads. Gennett struck out pinch- hitting in the ninth.
Cardinals: Outfielder Jon Jay missed his fifth straight start with a sore wrist from a checked swing in San Diego. he had to be extra disappointed, given he's 8 for 13 with a homer against Garza.
Brewers: Milwaukee awaits the Giants, with Jimmy Nelson (1-2, 4.30) facing Tim Lincecum (9-7, 4.21) on Tuesday at Miller Park.
Cardinals: After an off-day, the Cardinals host Boston for a three-game series beginning Tuesday night. On Wednesday, Shelby Miller (8-8, 4.14) faces ex-teammate and close friend Joe Kelly (2-2, 4.37), who was traded to Boston in the Lackey trade. Miller and Kelly were the best man in each other's wedding.
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