Game 4 wasn't half-bad as OKC shot 53.8 percent in the first half to take a 56-48 lead at intermission.
As has been the case much of the series, the Thunder faltered in the second half, shooting just 37.5 percent from the floor.
Memphis outscored OKC 9-3 in overtime as the Thunder shot just 1 for 8 from the field with Kevin Durant going 0 for 5.
Grizzlies center Marc Gasol swished a 15-footer with 22.8 seconds left in overtime to give the Grizzlies a 100-97 lead.
Memphis guard and former Oklahoma State standout Tony Allen essentially sealed the win by stealing the ensuing inbound pass from Derek Fisher. Gasol added another free throw with 20.8 seconds left.