Rusin (2-1) twice worked out of bases-loaded jams and only set the Cardinals down in order in the first. He struck out a season-high five and issued two intentional walks.
Kevin Gregg recorded his 24th save to complete the Cubs' first shutout in St. Louis since Jeremi Gonzalez tossed one on June 23, 1997.
Lance Lynn (13-6), attempting to become the National League's first 14-game winner, labored over 6 2-3 innings despite giving up just three hits. He threw 115 pitches and was charged with all three runs. He struck out five, walked five and hit two.
Chicago has won two of three, but only has three wins in its past 12.
St. Louis has lost four of five and 12 of 16. The Cardinals have been shut out four times during that span and have scored three or fewer runs 10 times, despite getting 13 runs in two victories and 15 runs in a third.
Lynn's night ended after he plunked Cole Gillespie to load the bases in the seventh with two outs. Lefty Randy Choate came in to face the left-handed Rizzo, who singled to center on a two-strike pitch to score Darwin Barney and Junior Lake and make it 3-0.
The Cubs opened the scoring on Lake's two-out single that scored Welington Castillo, who walked to open the seventh.
It could have been more. Starlin Castro was originally called safe by first base umpire Larry Vanover on a bunt that Lynn fielded and applied the tag. After a short argument from Cardinals manager Mike Matheny, the umpire crew gathered and reversed the call for the first out of the inning.
Rusin twice intentionally walked Pete Kozma to load the bases with two outs and face Lynn. Lynn struck out in the second and ended the fourth with a grounder.
Rusin was lifted for pinch-hitter Logan Watkins with runners at first and second with one out in the seventh. Watkins struck out.
Both managers tinkered with their lineups to try and boost their struggling teams.
The Cubs used David DeJesus in the cleanup position for the first time in his career. DeJesus struck out to end the seventh with runners at first and third and finished 0 for 3, with a walk and a hit-by-pitch.
The Cardinals moved David Freese to second in the order for the first time this season. He had a single in four at-bats.
NOTES: St. Louis pinch-hitter Daniel Descalso was ejected soon after arguing about a called third strike. Matheny came out to argue the ejection and was also tossed. ... Cubs C Dioner Navarro, injured in a plate collision with Philadelphia's Chase Hudley on Wednesday, will not go on the disabled list. He was diagnosed with a mild Grade 1 right ankle sprain on Friday and is listed day-to-day. . P Michael Wacha will start Saturday's game in lieu of Adam Wainright who was pushed back to Tuesday against first-place Pittsburgh. . Chicago P Matt Guerrier, placed on the 60-day disabled list Thursday with right elbow soreness, is expected to have surgery on his right elbow for what GM Theo Epstein called flexor mass, though Epstein ruled out ulnar collateral ligament reconstruction or Tommy John surgery. ... St. Louis OF Shane Robinson played in his first rehab game Friday since he went on the 15-day disabled list July 31 with a right shoulder strain. He was the designated hitter for Double-A affiliate Springfield (Mo.) . Friday marked the 25th anniversary of the first night game at Wrigley Field. The Cubs defeated the New York Mets 6-4 on August 9, 1988.
Link to box score: Chicago 3 at St. Louis 0
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