On the first pitch after a brief delay to carry the kitty off the field, Molina lined a grand slam to left field as St. Louis notched its fifth straight win with an 8-5 decision.
With two outs in the bottom of the sixth inning, Molina took a first-pitch ball from reliever Peter Moylan. Before the next pitch, Molina pointed out to left field, noticing the feline.
The cat made it all the way to the center-field wall before Lucas Hackmann, a member of the grounds crew, collected it. Hackmann was bitten a few times as he ran the cat into the stands.
Moments later, Molina lashed Moylan's sinker 387 feet to the seats for his 14th homer of the year and his fifth career slam. Before touching first, Molina jumped in the air, pumping his right fist for joy.
Cardinals first baseman Matt Carpenter, who was standing at second base as the cat pranced into the outfield, was convinced Molina was going to do something big after the delay.
"That was crazy," he said. "It is one of those weird things that happen. I felt good about our chances before the cat; but, after that, I knew Yadi would come through."
Before Trevor Rosenthal, St. Louis' sixth pitcher, worked a scoreless ninth to post his ninth save in 11 chances, #rallykitty had become a trending item on social media.
Some were comparing it to the squirrel that held up a playoff game with Philadelphia in 2011 just before a Cardinals rally staved off elimination during an unlikely run to their 11th World Series title.
"I thought it was a streaker, to be honest," Matheny said.
The only streaking going on in Busch Stadium is by the home team. It was the Cardinals' fifth straight win, a stretch in which they have outscored opponents 46-16. They scored 10 or more runs in the previous three games.
This victory came after Kansas City (57-56) opened a 3-0 lead against Mike Leake in the second inning. The Royals pieced together four hits to start the game, getting an RBI double from Lorenzo Cain and a run-scoring hit from Melky Cabrera.
They then tacked on a third run in the second when Molina threw the ball into center field trying to nail Cain on a steal attempt, allowing Whit Merrifield to score.
But the Cardinals (58-56) took advantage of wild Royals starter Trevor Cahill to tie the score before the third inning was over. They scored twice in the second on Leake's safety squeeze bunt and Carpenter's RBI hit, then equalized on Jedd Gyorko's single in the third.
Jose Martinez rifled a 419-foot homer to center off reliever Scott Alexander in the fourth to give St. Louis its first lead. But Cabrera jacked a two-run shot to right-center an inning later to regain a one-run edge for Kansas City.
However, the Royals' tired bullpen, which had to pick up 13 outs Tuesday and nine Monday after a Sunday doubleheader, couldn't hold the lead. Brandon Maurer (0-1) gave up a single to pinch-hitter Greg Garcia and walked Carpenter to start the sixth.
Moylan came in and got a flyout from Martinez, although the runners moved up on a throwing error by right fielder Jorge Bonifacio. After whiffing Paul DeJong, Moylan issued an intentional walk to Dexter Fowler.
That set the stage for Molina -- as well as the cat that became an instant celebrity.
"I heard the crowd erupt and I thought there must have been something on the scoreboard," Moylan said. "I turned around and there's a kitten running around, which is the first time that's happened to me."
Matt Bowman (3-4) pitched a scoreless sixth to garner the win as the Cardinals moved into a tie with Milwaukee for second in the National League Central, 1 1/2 games behind the Chicago Cubs.
Kansas City fell a game behind Seattle for the American League's second wild-card spot.
Leake was pounded for 11 hits and five runs (four earned) in five innings. He walked one and fanned five.
Cahill lasted only 2 1/3 innings, giving up three runs, four hits and five walks with a strikeout.
NOTES: St. Louis LF Tommy Pham didn't start for just the second time since the All-Star break. Pham did enter as a defensive replacement in the eighth inning and doubled, his first extra-base hit since July 24. ... Kansas City SS Alcides Escobar started his 284th straight game, tying Baltimore's Miguel Tejada (2004-05) for the longest streak in the majors at the position since the Orioles' Cal Ripken Jr. started 2,216 consecutive games from 1982 to 1996. ... Cardinals CF Dexter Fowler batted in the cleanup spot for the first time this year and only the 27th time in his 1,148 games. Fowler was 1-for-2 with three walks and two runs.