On Saturday, the two will duel again in Game 2 of a weekend I-70 Series in Kansas City.
Wainwright allowed one earned run on five hits over seven innings against the Royals. He allowed his only run on three straight, unlucky singles in the second inning. From there, Wainwright cruised, not allowing a hit until the sixth inning.
Mendoza threw five shutout innings before allowing back-to-back homers by Matt Holliday and Allen Craig in the sixth. He finished his day after the sixth, allowing six hits while fanning five and walking one.
Both clubs enjoyed the long-awaited returns of players from stints on the disabled list on Friday, which should help them offensively moving forward.
The Cards welcomed back center fielder Jon Jay and first baseman/outfielder Matt Carpenter, while catcher catcher Salvador Perez returned to the Royals' lineup.
Jay was on the 15-day disabled list and had seven Triple-A at-bats while recovering from a sprained shoulder. Carpenter was sidelined with a strained right oblique, and had 17 Minor League at-bats during his rehab assignment.
"I just personally hate not being a part of the club," Carpenter said. "You'd like to think that if you were here you'd be able to make an impact."
Jay went 1-for-5 with two runs scored in his return on Friday, while Carpenter finished 2-for-4 with a double and two runs scored in the Cards' 11-4 rout.
Perez, who underwent right knee surgery on March 16, was reinstated from 60-day disabled list, and went 2-for-4 with a two-run homer against the Cardinals.
"He's a guy that we are kind of hinging a bit of our future on," Royals manager Ned Yost said of Perez. "He's a very intelligent young man. I'm glad he's back."
Cardinals: Craig given night off
Allen Craig was out of the starting lineup on Friday while still experiencing soreness in his wrist after landing on it awkwardly during a diving attempt in the outfield against the Tigers on Wednesday.
Craig gave manager Mike Matheny the go-ahead to pencil him in at designated hitter after taking pregame batting practice on Friday, but Carpenter played first base and Carlos Beltran served as the designated hitter to give Craig the night off.
Prior to Friday's win, the Cardinals were batting .228 (23-for-101) with zero home runs and three RBIs in the first three games on their current road trip. St. Louis collected 17 hits on Friday and had five players with multi-hit games.
Royals: Tommy John likely for Paulino
Right-hander Felipe Paulino was diagnosed by team doctors on Friday with a torn ulnar collateral ligament in his right elbow -- an injury that commonly calls for Tommy John surgery.
Paulino will become the fourth Royals pitcher this season to undergo the procedure.
"There's going to be surgery. It's going to happen, Paulino said. "They gave me two options -- rest or surgery -- and I prefer to have surgery."
While Paulino anticipates having the surgery, he will however get a second opinion from Dr. Lewis Yocum, a specialist in the field.
Closer Joakim Soria, starter Danny Duffy and reliever Blake Wood all underwent Tommy John surgery this season.
Entering Friday's contest, Royals pitchers posted a 3.32 ERA in their last 39 games since May 8, the fifth-best mark in the Majors and third-best in the American League. Before that stretch, Kansas City's pitching staff ranked 27th in baseball with a 4.96 ERA through May 7.
The Royals took two of three from the Cardinals in St. Louis last weekend. St. Louis leads Kansas City, 40-30, all time in regular-season matchups, including a 25-15 advantage at Kauffman Stadium.