Wainwright (7-5) scattered seven hits, walking two and fanning five in recording his 13th career win against Milwaukee -- tying his most against any opponent. It was his first outing against the Brewers since rupturing his Achilles' tendon on April 25, 2015 in Milwaukee, an injury that cost him all but the final week of last year.
Jonathan Broxton worked the eighth and new closer Seung Hwan Oh retired the Brewers in order in the ninth for his first save as St. Louis (42-38) beat Milwaukee (35-45) for the sixth time in eight meetings this year.
Wong snapped a scoreless tie in the bottom of the fourth, lining a 2-2 pitch from Jimmy Nelson (5-7) into right-center field. Right fielder Ramon Flores' head-long dive produced nothing but air and the ball rolled to the wall as Stephen Piscotty and Yadier Molina scored.
Greg Garcia capped the scoring with a squeeze bunt single that plated Wong.
Nelson lasted six innings, allowing seven hits and three runs, two earned. He walked two and fanned six.
In falling to 13-25 on the road, the Brewers didn't lack for opportunities. They started four straight innings with leadoff singles, but Wainwright cut off three of those potential threats with double-play grounders.
Milwaukee got just one runner to third base, that being Hernan Perez in the seven after he singled with one out, stole second and reached third on Flores' groundout. But Wainwright fanned pinch-hitter Jake Elmore with a 3-2 cutter.
The game was delayed for 92 minutes at its start by persistent showers, and was played in varying degrees of rain for most of its 2 hours and 40 minutes.
NOTES: St. Louis 3B Matt Carpenter missed Saturday's game due to a death in his family, but was expected to return for Sunday's game. ... Milwaukee 1B Chris Carter's homer in the second inning Friday night made him the 12th player in franchise history to reach 20 homers before the All-Star break. ... Cardinals RF Stephen Piscotty (ankle) returned to the lineup Saturday after a two-game absence. He was injured sliding for a ball in the 12th inning of Wednesday night's loss to Kansas City.