Marcos Ambrose claimed his second successive win at Watkins Glen after emerging up front from a thrilling last-lap battle with Brad Keselowski and Kyle Busch.
Fluids on the track during the last two laps threw the NASCAR Sprint Cup race wide open after Busch had looked set to claim a victory that would have solidly placed him as a Chase contender.
Ambrose was the first to slip in the tricky conditions in the inner-loop section, allowing Keselowski to get a run on him, the Penske driver taking advantage and passing the Richard Petty Motorsports Ford to claim second place.
Ahead of him Busch also struggled with the lack of grip, apparently caused by Bobby Labonte's car leaking oil, and thus a safe 2.3-second cushion suddenly turned into less than a second going into the final lap.
Busch then went wide into Turn 1 and Keselowski tried to dive down his inside entering Turn 2, but the Joe Gibbs driver ended up spinning and hitting the guardrail after the right-rear of his Toyota got clipped by the Dodge's left-front.
Ambrose then performed a similar move on Keselowski, getting the lead out of the Carousel section, although his rival was able to keep the pressure on, hitting the back of the RPM Fusion under braking for the penultimate turn.
The former Australian V8 Supercars champion ran wide on the exit as a consequence but was able to get the inside for the final turn, entering side-by-side with Keselowski, and crucially coming out ahead as his rival got sideways on the slippery surface.
"I was the first one to slip in the oil and it was just getting worse and worse," said Ambrose. "You could tell the car was staying out there because the oil was moving around the racetrack and you just take your chances.
"You've got to commit at that point in the race and it was great racing with Kyle and Brad. They're the two best guys to race. It's just awesome fun and that's the way racing should be."
Keselowski enjoyed the battle for victory so much that he did not seem to mind losing a possible fourth win of the season on the final lap.
He lamented the contact with Busch but said he hoped his rival understood his position as victory was at stake.
"The core of the sport and why people come to watch is to know that we're going to give it our all any given day," said Keselowski. "If the day comes when we don't do that, we're no longer racers... that's our job."
Hendrick Motorsports' Jimmie Johnson ran a solid race to third and claimed the points lead from his team-mate Dale Earnhardt Jr, who spun a few laps from the end and finished 28th.
Jeff Gordon was set for a top-10 result after struggling with handling initially but a spin on the last lap caused him to finish only 21st, temporarily losing his wildcard status for the Chase to Stewart-Haas' Ryan Newman.
Five-time Watkins Glen winner Tony Stewart was in contention for victory but he spun at the final turn after clipping the inside kerb, 18 laps from the end while running second.
Polesitter Juan Pablo Montoya had a rough end to his day after a front suspension control arm broke while he was running fifth.
JGR's Denny Hamlin finished the weekend on the sidelines after an engine failure on lap 50, causing the fourth of five caution periods to wave.
A brief shower forced the pace car to stay out longer than planned during the caution before conditions were good enough again to resume racing.
Results - 90 laps:
Pos Driver Team/Car Time/Gap
1. Marcos Ambrose Petty Ford 2h14m48.000s
2. Brad Keselowski Penske Dodge + 0.571s
3. Jimmie Johnson Hendrick Chevrolet + 9.218s
4. Clint Bowyer Waltrip Toyota + 9.269s
5. Sam Hornish Jr Penske Dodge + 9.493s
6. Greg Biffle Roush Fenway Ford + 10.289s
7. Kyle Busch Joe Gibbs Toyota + 10.489s
8. Matt Kenseth Roush Fenway Ford + 11.124s
9. Regan Smith Furniture Row Chevrolet + 11.555s
10. Martin Truex Jr Waltrip Toyota + 12.631s
11. Ryan Newman Stewart-Haas Chevrolet + 12.940s
12. Paul Menard Childress Chevrolet + 12.999s
13. Kasey Kahne Hendrick Chevrolet + 13.076s
14. Carl Edwards Roush Fenway Ford + 13.584s
15. Kevin Harvick Childress Chevrolet + 16.460s
16. Casey Mears Germain Ford + 16.934s
17. Scott Speed Leavine Ford + 16.976s
18. Aric Almirola Petty Ford + 17.050s
19. Tony Stewart Stewart-Haas Chevrolet + 23.560s
20. David Gilliland Front Row Ford + 23.721s
21. Jeff Gordon Hendrick Chevrolet + 24.430s
22. David Ragan Front Row Ford + 26.547s
23. Landon Cassill BK Toyota + 37.988s
24. Travis Kvapil BK Toyota + 38.259s
25. Boris Said FAS Lane Ford + 1m13.902s
26. Stephen Leicht Circle Sport Chevrolet + 1m20.259s
27. Bobby Labonte JTG Daugherty Toyota + 1m28.469s
28. Dale Earnhardt Jr Hendrick Chevrolet + 1 lap
29. Joe Nemechek NEMCO Toyota + 2 laps
30. Jeff Burton Childress Chevrolet + 6 laps
31. Kurt Busch Phoenix Chevrolet + 9 laps
32. Joey Logano Joe Gibbs Toyota + 19 laps
Juan Pablo Montoya Earnhardt Ganassi Chevrolet 63 laps
Denny Hamlin Joe Gibbs Toyota 57 laps
Jason Leffler Robinson-Blakeney Toyota 42 laps
Dave Blaney Baldwin Chevrolet 41 laps
Michael McDowell Parsons Ford 30 laps
Josh Wise Front Row Ford 25 laps
Jamie McMurray Earnhardt Ganassi Chevrolet 24 laps
JJ Yeley Baldwin Chevrolet 15 laps
Chris Cook Humphrey Smith Toyota 5 laps
Patrick Long Inception Toyota 2 laps
Brian Vickers Waltrip Toyota 0 laps