The unbeaten Cowboys advanced to the finals of the Old Spice Classic in Kissimmee, Fla., where they will face either LSU or Memphis.
Butler trailed by 14 points at halftime, but rallied down the stretch and had multiple opportunities to either tie the game or win it. Oklahoma State almost let the game get away when it managed just one point over the final 4:20.
Butler's Khyle Marshall went to the foul line with eight seconds left and his team trailing by only one, but he missed both tries and the Cowboys' Le'Bryan Nash seized the rebound.
Nash was immediately fouled and he could make just 1-of-2 from the line.
That gave Butler a chance to win it with a 3-pointer, which Brown attempted as time ran out. Cobbins was there for the block, however, giving Oklahoma State its seventh win in as many games. Butler fell to 5-1.
Marcus Smart led the Cowboys with 17 points and Nash had 15. Brown came off the bench to score 15 for the Bulldogs.