Nyman stole third base, and designated hitter Bryan Verbitsky's infield single drove him home to tie the game.
OU sophomore Robert Tasin earned the win after pitching a perfect ninth inning to set up Oberste's heroics.
Hofstra (0-4) pushed Oklahoma in the series' final three games. The Sooners won Friday's opener handily, but sneaked by Hofstra 3-2 and 11-10 in a doubleheader Saturday, needing a huge rally and extra innings in the second game.
“We won every game in every way possible,” said senior catcher Max White, who was 3 for 4 with two RBIs Sunday. “We beat them pretty good, then we had a close game, had to close it off. Then we came back, then we just won it like that.
“That's all the ways in baseball you can win.”