"My defense came to my rescue every time I needed them to," Flaherty said. "That was the difference today."
Flaherty tossed seven scoreless innings, Yadier Molina drove in three runs and the Cardinals beat the Reds 5-2 on Sunday, taking two of three from their NL Central rivals.
Jose Martinez had two hits and drove in a run for the Cardinals, who have won seven of eight overall.
Scott Schebler hit a two-out, two-run double in the ninth for the Reds, who have lost three of five.
Molina extended his hitting streak to 15 games, one short of his career best, with a bases-loaded single in the eighth.
Flaherty (3-1) gave up four hits in an 89-pitch outing. He struck out four and walked one. He was helped by three double plays, two of which ended innings.
"I loved his tempo, loved his aggression, loved his game plan," St. Louis manager Mike Shildt said. "He had a lot of quality pitches in the strike zone."
Molina said Flaherty was locked in from the outset.
"He was throwing first-pitch strikes," Molina said. "That slider was obviously the best pitch he had."
Flaherty said the biggest defensive play of the game was second baseman Kolten Wong's diving catch of a line drive by Tucker Barnhart that ended the first inning. Flaherty walked Yasiel Puig with two away after getting ahead in the count 0-2.
"That was frustrating," Flaherty said.
Wong's play set the tone for the rest of Flaherty's day.
"We got a lot of momentum after that," Flaherty said. "Those guys made every single play."
St. Louis scored twice in the fourth off Sonny Gray (0-4), who gave up three hits in five innings. He struck out five and walked two.
Martinez has worked his way into the starting lineup and went 14-for-32 (.438) during St. Louis' nine-game homestand.
"Every chance they give you, you have to take advantage," Martinez said.
Wong started a three-run outburst in the eighth with a double to right that Puig lost in the sun.
Joey Votto reached base twice for the Reds, who are 10-8 since a 1-8 start to the season.
Gray, making his first career appearance against the Cardinals, set down the first six batters and struggled in only one inning.
"I got zero swings on my breaking balls and that's normally my best pitch," Gray said. "I didn't quite have a feel for it today."
END OF THE LINE
Paul Goldschmidt had a 13-game hitting steak snapped.
Cardinals: RHP Alex Reyes was placed on the 10-day injured list with a broken left pinkie. The 24-year-old punched a wall in frustration after his outing with Triple-A Memphis on Thursday. Reyes gave up three runs on three hits in 2 2/3 innings at Omaha. "He made a decision that I'm sure he would choose to do over," Shildt said. "He cares."
Reds: RHP Tanner Roark (1-1, 3.42 ERA) will start on Monday against the New York Mets. Zack Wheeler (2-2, 4.85) will pitch for the Mets in the first of a four-game set. Roark is 8-4 with a 3.07 ERA in 22 career starts against New York.
Cardinals: RHP Michael Wacha (1-0, 4.64) starts in the opener of a four-game series at Washington on Monday against LHP Patrick Corbin (2-0, 2.48). Wacha will be coming off the 10-day injured list. He missed one start because of left knee patellar tendinitis.
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