Irving hit back-to-back 3-pointers after Oklahoma City had taken a 63-50 lead midway through the third quarter. His driving layups on consecutive possessions got Cleveland within 67-65 with 3:42 to go in the period.
The Thunder's Kendrick Perkins protected the lead by scoring inside on a basket interference call before Westbrook set up Durant's two-handed slam.
Even though Westbrook hadn't scored in the first 9 minutes after halftime, Brooks didn't take him out for his usual break at the end of the third quarter.
"My gut was telling me to keep him in there," Brooks said. "He didn't play a lot of minutes in the first half, so I knew that I had some extra minutes in him. I just felt that we needed his toughness in tonight's game."
Westbrook rewarded him with a jumper in the lane and a 3-pointer to help fend off Irving's onslaught, and it only got better from there. Including the desperation shot, Westbrook made four straight 3-pointers when it counted the most.
"He's worked on it. He's going to continue to work on it," Brooks said. "That one was probably a lucky shot but other than that, they were shots he can make."
Kevin Martin led Oklahoma City's reserves with 16 points and Serge Ibaka had 14 points and seven blocks. Westbrook had 10 assists but also eight turnovers.
The Cavaliers hit eight of their first 10 shots and raced out to a quick 17-7 lead, but then fell just as cold as they had been hot as soon as Waiters checked out with his second foul. Eight of Cleveland's next nine shots were off-target, giving the Thunder the opening they needed to pull ahead for good.
Westbrook converted a finger roll and a jumper and set up Thabo Sefolosha's 3-pointer during a 15-2 comeback, and Oklahoma City kept rolling against Cleveland's reserves. Martin had a three-point play and a fast-break layup early in the second to make it 34-23.
NOTES: The Cavs were Oklahoma City's second straight opponent that was playing the fifth game of a six-game road trip. ... Daniel Orton made his first appearance with the Thunder with the game out of hand in the final 2 minutes. He blocked a Gibson 3-pointer and got his first points by running out for a layup at the other end. ... Orton was active because backup center Hasheem Thabeet missed his second straight game with a sprained left ankle.