Blair sprung free for a layup early in an 18-5 comeback, and Ginobili's 3-pointer from the top of the key trimmed Oklahoma City's lead to 73-71 with 1:16 to go in the third quarter.
The Spurs were within four after Duncan's left-handed runner with 6:55 left in the game. That's when Thunder coach Scott Brooks called a timeout, and Durant came out of it firing away. He made seven of his last eight shots and also finished with eight assists and six rebounds.
"It was hard because were on a run, we were feeling good about ourselves and we just couldn't make a stop," Ginobili said.
Ibaka made all 11 of his shots — and all four of his free throws — to lead a strong performance from Oklahoma City's frontcourt while Durant's usual running mates, Westbrook and Harden, both struggled.
Ibaka, starting center Kendrick Perkins and reserve Nick Collison combined to go 22 for 25 from the field for 49 points. Westbrook missed eight of his 10 shots and Harden was limited to eight points.
The Thunder shot 56 percent and outrebounded San Antonio 41-31.
Oklahoma City pulled ahead to stay with a 12-3 run early in the second quarter with Durant and Westbrook both taking a break. Westbrook nailed a 3-pointer from the left side soon after returning to provide the Thunder's first double-digit lead at 43-33 with 4:44 to go before halftime.
NOTES: After committing a postseason-worst 21 turnovers in Game 3, San Antonio had 10 that led to 11 Oklahoma City points. ... Ryan Seacrest sat in the front row near midcourt.