Lynn (4-4) was brilliant in his outing, scattering five hits and striking out five in 7 2/3 scoreless innings.
Matt Holliday had his streak of reaching base safely to begin the season halted at 45 games after he was ejected in an 0-for-3 effort. The streak was the fifth longest to begin a season in MLB history and his 47 straight games dating back to last season was eight off Stan Musial's club record set in 1943.
Tyler Cravy (0-1), making his MLB debut, was charged with one run on four hits with six strikeouts in seven innings.
After getting blanked 1-0 in the series opener, St. Louis got on the board with one in the second. Randal Grichuk doubled with one out and Reynolds singled two batters later for a 1-0 lead. Reynolds was thrown out at second to end the inning.
Lynn, meanwhile, needed just that as he limited just two Brewers to reach second through seven innings.
In the home seventh, Holliday's streak ended after he was thrown out by homeplate umpire Joe West for arguing balls and strikes. Cardinals manager Mike Matheny was then subsequently ejected for coming to Holliday's defense.
Trevor Rosenthal pitched the ninth and ran into some trouble. Ryan Braun reached on an infield single to shortstop, and Jonathan Lucroy followed a popout from Adam Lind by shooting a base hit into right that put runners on the corners. Rosenthal worked out of trouble by rolling a 5-4-3 double play off the bat of Aramis Ramirez to secure his 16th save of the season.