Westbrook scored 33 points and Kevin Durant added 23 points and 13 rebounds as the Thunder beat the Dallas Mavericks 95-86 on Wednesday night.
Ibaka had a career-high 10 blocked shots, helping Oklahoma City limit Dallas to 8-for-38 shooting from the field in the second half.
"He was amazing," Thunder coach Scott Brooks said of Ibaka, who also had 11 rebounds. "He's been playing great defense eight of the last nine games."
Jason Terry had 26 points for the short-handed Mavericks, who snapped a three-game winning streak.
Dirk Nowitzki went 2 for 15 from the floor and finished with eight points for Dallas in his third game back after a four-game absence to deal with a sore right knee and conditioning issues. He had 10 points in each of his first two games after returning.
"I had some good looks," said Nowitzki, last season's MVP of the NBA finals. "I've just got to keep working."
Nowitzki said his knee is better than it was two weeks ago, "But sometimes I don't have enough confidence in my movement if I try to make a hard move."
Oklahoma City has won two of three meetings between the teams this season. The Mavs took a five-game series with the Thunder in last season's Western Conference finals before Dallas went on to its first league title.
Mavericks coach Rick Carlisle was ejected with 9:34 left in the game after picking up two technicals in a span of about two minutes. The second was assessed after Carlisle kicked the game ball into the stands in frustration during a stoppage in play after a no-call that went against his team.
Carlisle apologized to owner Mark Cuban and the fans after the game, saying, "The incident where the ball got kicked into the stands, that can't happen. My intent was not to kick it into the stands. I was trying to kick it to the referee, but I'm not a very good kicker. ... That's a regrettable situation."
Dallas starting point guard Jason Kidd sat out his third straight game with a strained right calf.
The Mavericks trailed by 10 early in the fourth quarter before rallying to tie it at 85 on Shawn Marion's runner in the lane with 2:14 left.
But Westbrook and Durant connected on consecutive mid-range jumpers, then Westbrook made a 3 from the right wing with 35 seconds to play to give his team a 92-85 advantage.
The Thunder fought back from a nine-point first-half deficit, grabbing a 59-56 lead with 7:25 remaining in the third quarter on consecutive layups by Westbrook. That sparked a 10-2 spurt that put the Thunder ahead 65-58, and Oklahoma City carried a 71-66 edge into the final quarter.
The Ibaka-led defense held Dallas to 3-for-19 shooting from the floor in the third quarter.
Ibaka blocked three shots in the third after swatting four in the second quarter, surpassing his season-high of seven before getting two more early in the fourth to beat his career high of eight.
"Serge was fun to watch," Durant said. "(Nowitzki) missed some shots he normally hits....I think we frustrated him."
Dallas got off to a fast start, hitting nine straight field-goal attempts during one stretch in the first quarter to build a 29-21 lead entering the second quarter.
The Mavs went 13 for 19 from the field in the first quarter while the Thunder connected on only 6 of 19.
Oklahoma City got back in the game with a 16-7 second-quarter run for its first lead of the night, 37-36 on Durant's 16-footer with 7:12 left until halftime.
Dallas held a 52-49 advantage at the break on Roddy Beaubois' reverse dunk with 29 seconds left and Marion's follow with less than a second remaining.
Carlisle said Ibaka set a tone with his second-quarter defense after the Mavs got off to such a positive offensive start.
"It was very disruptive," Carlisle said. "The blocks he had in the second quarter, I thought were really the difference in the game if you look at the big picture."
Dallas entered the night having won nine of 10 at home since opening the season with consecutive losses. ... Oklahoma City was minus starting swingman Thabo Sefalosha due to a sore right foot. The Thunder were also without reserve G Eric Maynor (torn right knee ligament).