Skidding around the 11-turn, 2.45-mile layout, Ambrose and Keselowski battled side by side nearly all the way around. Both even went into the grass in the inner loop at the top of the esses but kept charging.
''I knew there was oil all over the bus stop (inner loop),'' winning crew chief Todd Parrott said. ''It looked like the cars went through the grass because there wasn't any oil.''
Ambrose slipped again in Turn 10, but Keselowski couldn't drive past. Neither gave ground, and Ambrose forged ahead 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.''
Busch was not available for comment after the race.
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, which is leaving NASCAR at season's end, 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 - provided they finishing 20th or higher in points.
Polesitter Juan Pablo Montoya, who broke the track record in qualifying, finished 33rd after being forced to pit when something broke in the right front of his No. 42 Chevy a third of the way into the 90-lap race. He had tracked Busch for the first 26 laps.