No sooner did the Red Sox take a 2-1 lead thanks to David Ortiz's long home run into the Green Monster seats in the bottom of the sixth inning of Game 2 than the Cardinals put together a rally of their own in the top of the seventh. After Allen Craig struck out looking, David Freese worked an eight-pitch walk and Jon Jay singled him to second, driving Boston starter John Lackey from the game after 95 pitches.
With lefty Craig Breslow on the mound, St. Louis manager Mike Matheny, partially due to his lean bench, stuck with lefty ninth-place hitter Daniel Descalso but pinch-ran righty-hitting shortstop Pete Kozma for Freese at second base. Kozma and Jay stole third and second, respectively, and Descalso took an impossibly close slider on the inside corner for ball four to load the bases.
Matt Carpenter then lifted the first pitch he saw to medium leftfield. Kozma tagged and the result is what you see in the GIF above: a game-tying sacrifice fly and a throwing error by Breslow backing up the plate that allowed Jay to come home with the go-ahead run (and for Descalso to get to third).
Carlos Beltran followed by singling home Descalso to make it 4-2 and just like that the Cardinals had their biggest lead of the night.