Westbrook (3-2) worked around trouble almost the entire night in his second start since coming off the disabled list with a sore elbow. He gave up no earned runs, striking out two and walking three.
Edward Mujica pitched a perfect ninth inning for his 21st save in 21 attempts.
Allen Craig reached in the fifth after second baseman's Darwin Barney's throw on the back end of a double-play attempt went to the Cardinals dugout. Molina drove a 1-2 pitch just over the outfield wall to improve to 9 of 15 with three homers against Jackson.
Westbrook retired the Cubs in order in the first and seventh innings, allowing at least one to reach in the five innings between. He faced the minimum in three of those five innings. Two runners were erased on inning-ending double plays and Luis Valbuena was caught stealing on a pitch out for the first out of the third.
Anthony Rizzo opened the second with a single and went to third when second baseman Matt Carpenter's throw to start a potential double play sailed over the Kozma's head and into leftfield. Rizzo tagged up on a sacrifice fly from Barney and scored after knocking the ball out of Molina's glove.
Carpenter singled to start the first and scored on Craig's hit to center.
NOTES: The Cardinals earned at least a split of the four-game series. ... Jackson's exit with one out in the fifth snapped a five-game streak in which the Cubs' rotation recorded a quality start and a seven-game stretch in which it went at least six innings. . Craig is hitting .431 with runners in scoring position. . Rizzo's single in the second ended a 0-10 streak. . Molina was assessed with his third of the year error for dropping the ball in the second and allowing Ryan Sweeney and Welington Castillo to advance. He had three all of last season. . Major League Baseball made two scoring changes from the Cardinals' game June 11 at the New York Mets. It rewarded Molina a double rather than an error as originally scored and changed an error assessed to 3B David Freese to a hit for David Wright.
Link to box score: St. Louis 4, Chicago 1
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