Arrieta (1-0) allowed two hits and struck out seven for his first win with the Cubs.
The hard-throwing right-hander was acquired from the Baltimore Orioles in a July 2 trade.
Before Friday, his only other day on the Cubs' roster was as the 26th man for a doubleheader against Milwaukee on July 30.
The Cubs snapped a four-game losing streak with the win and are 7-7 this season against the Cardinals. St. Louis has dropped six of nine overall.
The Cubs had been shut out in four of their past five home games - a streak dating back to Aug. 3.
Cardinals starter Jake Westbrook (7-8) walked the first three batters he faced in the bottom of the first inning.
Schierholtz, the cleanup hitter, hit a two-run single to center to put the Cubs.
Those two outs started a streak of 13 straight outs (including five strikeouts) until he walked Westbrook with one in the sixth.
The Cubs added a run in the fifth on Schierholtz's sacrifice fly and then scored two more in the sixth on a run-scoring double by Darwin Barney and a safety squeeze bunt by Arrieta.
The final run in the seventh scored on a Sam Freeman wild pitch.
NOTES: With the addition of prospect Kolten Wong (who went 0-for-3 in his debut) to the Cardinals' roster and lineup on Friday, former World Series MVP David Freese was relegated to the bench with leadoff hitter Matt Carpenter (who had been playing second) moving to third base. ''I would say it's a day-by-day situation,'' general manager John Mozeliak said. ''I'm not saying (Wong) has to play every day - there are gonna be times when we want to get David back in the lineup - so I imagine there's gonna be some split playing opportunities.'' ... Cubs RHP Matt Guerrier was scheduled to have surgery on his throwing arm on Friday. The surgery, performed by Dr. Timothy Kremchek, is expected to sideline Guerrier six to eight months. ... The Cards' Joe Kelly (3-3) faces Travis Wood (7-9) in the second game of the series on Saturday.
Link to box score: Chicago 7, St. Louis 0
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