Kyle Busch, desperate for a win to move back into contention for the Chase for the Sprint Cup championship, was in control of the race but was leaking oil on the track. He skidded sideways coming out of the first turn of the final lap. Keselowski's No. 2 Dodge caromed off the side of the No. 18 Toyota and Ambrose followed Keselowski through.
"Busch slipped up big in turn one," said Keselowski, who suffered damage to the front of his car. "There was nothing he could do. We all checked up and Marcos was right on my bumper. We all just about spun out. We got to the inner loop, and again nothing but oil."
Slipping and sliding around the 11-turn, 2.45-mile layout, Ambrose and Keselowski battled side by side nearly all the way around. Both went into the grass in the inner loop at the top of the high-speed esses but kept charging.
Ambrose slipped again in turn 10, but Keselowski couldn't drive past. Neither gave ground, but Ambrose forged ahead in his Richard Petty Motorsports Ford on the final turn, another hard right-hander, and turned away Keselowski's final charge on the outside.
"I must have hit the oil one more time and he didn't," Keselowski said. "I thought I had him, but I hit more oil than Marcos did."
Entering the race, Ambrose had one win and had never finished lower than third in four starts at The Glen for an average finish of 2.3 and an average green flag speed of nearly 120 mph. Both were tops in the series.
Jimmie Johnson was third to gain the points lead by one over Greg Biffle. Sonoma winner Clint Bowyer and Sam Hornish Jr. were next, giving Dodge two in the top five. Dale Earnhardt Jr. spun late and finished 28th to fall from first to fourth in points, 17 behind Johnson.
Biffle was sixth, and Busch, Matt Kenseth, Regan Smith and Martin Truex Jr. rounded out the top 10. Ryan Newman finished 11th to move back ahead of Jeff Gordon into the second wild card slot. Kasey Kahne, who has two wins, holds the other. Gordon was also a victim of the oil, spinning late and dropping to 21st after having driven past Newman.
The top 10 drivers in the standings qualify for the 10-race Chase, and two wild cards are awarded to the drivers with the most wins outside the top 10. Only those in the top 20 are eligible for wild cards.
Last year, Ambrose beat Busch and Keselowski on a paint-trading two-lap dash to the checkered flag. Ambrose passed Keselowski for the lead on the final lap and secured his first Cup victory when a violent crash involving David Reutimann and David Ragan precipitated a caution that prevented Keselowski from making one final challenge.
Busch had the lead in that race, and he learned his lesson well. With all three up front again on a restart Sunday with 16 laps remaining in the 90-lap race, Busch dived from third to first on the inside of the 90-degree right-hander, outbraking both Ambrose and Keselowski to take the lead for the first time since lap 26.
Busch, who took the lead from pole-sitter Juan Pablo Montoya as soon as the green flag flew, kept Keselowski at bay off his back bumper, with Ambrose seven car lengths back, and pulled out to a 1-second lead as Ambrose challenged Keselowski for second. Ambrose finally got past him in the inner loop on lap 81, but he was 2.3 seconds behind and seemingly running for second until the dramatic finish.