Ambrose, who drives for Richard Petty Motorsports, pushed past Brad Keselowski on the next-to-last lap and won the Sprint Cup race at Watkins Glen, N.Y. The race was moved to Monday because of poor weather over the weekend.
“This is almost surreal,” said Ambrose, the fifth first-time Sprint Cup winner this season — the most since 2002. “It’s just a dream come true.”
Ambrose had won three Nationwide races at the Glen. “I've tried for 2½ years," Ambrose said. "We're going to onward and upward from here. It's a proud day.”
Keselowski took second and Kyle Busch was third, followed by Martin Truex Jr., Joey Logano, Kevin Harvick, Juan Pablo Montoya, A.J. Allmendinger, Jeff Burton and Jimmie Johnson.
Last-lap crashes, which included Tony Stewart, David Reutimann and David Ragan, brought out a yellow caution flag at the end.