But replays, and perhaps a mix-up in a rules interpretation by the umpires plus a slow response by Cincinnati, revealed St. Louis shouldn't have won the game when it did.
Molina's line shot off reliever Blake Wood (6-5) one-hopped off signage behind the left-field wall, but the ball was ruled in play. Matt Carpenter, who started the rally with a one-out walk, scored all the way from first.
Had the ball been properly called a ground-rule double, Carpenter would have been placed at third and Stephen Piscotty would have batted with the score still tied. Instead, the Bill Miller-helmed umpiring crew left the field about 30 seconds after Carpenter scored.
Shortly after that, Reds manager Bryan Price jogged out of his dugout and toward the umpires' dressing room to ask for a review, but it was denied.
"How do you let a game -- any game, but for this game that has playoff ramifications -- end because you won't wait more than 10 seconds on the field?," Price said. "I mean, that's ridiculous. That's a game-ending play. I'm not blaming the umpires, but how are we supposed to define in 10 seconds?"
"It definitely hit the sign," Cincinnati left fielder Adam Duvall said. "I saw it, I heard it."
While several Reds lingered in their dugout, hoping against hope, the Cardinals (83-76) celebrated the season's biggest and most controversial win. It pulled them within two games of the New York Mets for the National League's first wild-card spot.
More importantly, they drew within a half-game of San Francisco for the second wild-card position, pending the outcome of the Giants' home game with Colorado.
"I didn't know what happened," Molina said. "I came inside and they said it was a ground-rule double. ... it's been an up-and-down season but we got a big win."
Speaking to a pool reporter after the game, Miller said Price didn't indicate quickly enough that he wanted a review.
"I looked into the Cincinnati dugout and Bryan Price made no eye contact with me whatsoever," said Miller, the plate umpire. "And then, after 30 seconds, he finally realized someone must have told him what had happened, and we were walking off the field."
Miller also said that after viewing the play in the dressing room, the ball did hit the signage and should have been killed.
But it wasn't, and the result enabled Seung Hwan Oh (6-3) to pick up the win despite allowing the tying run in the top of the ninth. Pinch-hitter Scott Schebler rolled a two-out, two-strike infield single down the third base line to score Ramon Cabrera.
The Reds (67-92) pulled within 3-2 in the eighth when Duvall grounded a single to right that scored pinch-runner Tyler Holt. He replaced Joey Votto, who left the game after being hit in the chin by a throw from left as he legged out a leadoff double, his third hit of the night.
Molina and Jedd Gyorko cracked solo homers for St. Louis, which got another good start from 22-year old rookie right-hander Alex Reyes. He scattered seven hits in six innings and allowed one run, walking two and fanning six.
Cincinnati right-hander Dan Straily went six innings as well, yielding six hits and three runs with two walks and seven strikeouts.
But the only storyline anyone wanted to discuss after this one was the premature ending that was allowed to stand.
"That's ludricrous," Price said. "I tell you, the San Francisco Giants are going to be all sorts of upset about this one."
NOTES: Mired in a 7-for-95 slump dating back to Aug. 27, St. Louis LF Brandon Moss didn't start Thursday night as Jose Martinez replaced him. ... Cincinnati 2B Brandon Phillips (left hand) and CF Scott Schebler (hamstring) didn't start for the second straight game, with Hernan Iribarren and Ivan De Jesus, Jr. filling in. ... Cardinals 2B Kolten Wong (shoulder), who pinch-hit a leadoff triple in the ninth inning Wednesday night, didn't start for the sixth straight game. He was injured Friday after losing his balance in left field while trying to catch a liner.