It was a move of desperation for Busch, who needs a second win to ensure a spot in the Chase. He pulled away in the No. 18 Toyota, building up a two-second advantage with two laps remaining. But his lead slipped away due to oil dumped in the track's groove. Keselowski caught him on the 90th and final lap in Turn 1, bumping him out of the way, and beginning a wild run to the checkered flag.
"It was chaos," third-place finisher Jimmie Johnson said. "Those last two laps were just out of control with the oil down. You were studying the road trying to see if you can see an oil trail and there really wasn't a large visible one to dodge. But you could feel the oil on your tires and slipping and sliding and then guys are spinning all over."
Ambrose and Keselowski ran side-by-side for some of that wild, crazy last lap and it was the Australian who proved to be the best oil-meister with a pass on the final corner to win for the second straight year at Watkins Glen.
The final lap may have been the most entertaining of the Cup season, but it was a disaster for Busch.
Here are five things we learned at The Glen:
1. Ambrose extended the list of wild card contenders. Ambrose's first victory of the season allowed him to join Ryan Newman, Kyle Busch, Jeff Gordon and Joey Logano in the group with one win and in the top-20 in points. It's a logjam for that second wild-card spot behind Kasey Kahne, who has two wins. Newman is second in the wild card with four races in the regular season remaining, 13th overall in points and six in front of Busch and 10 in front of Gordon.
The only way for Ambrose to get there is a second victory. It's unlikely because they're all ovals and he's never won on an oval, but it gives him and Richard Petty Motorsports a shot.
? GALLERY: Sprint Cup winners of 2012
Ambrose's three pit-stop strategy left him in fifth for a restart with 22 laps to go and he went by both Clint Bowyer and Busch on it. But Ambrose had to drive his Ford so hard that he didn't have anything left for the final restart with 16 to go that put Busch in the lead.
"Our strategy was to do three stops and all of a sudden that caution came out and we had to pit," Ambrose explained. "We came in ninth or 10th or something and I just used the stuff up coming through and you just have to take Lady Luck when she strikes and it was our day."
Keselowski passed Ambrose for second halfway through the next-to-last lap.
"I slid into Turn 1 and I slid up the hill, and then I slid through the bus stop and allowed Brad to get past me, and I thought I was blowing up," Ambrose explained. "I thought it was my oil, not knowing what was really going on, and it wasn't until I saw Kyle and Brad sliding as well that I thought, 'OK, there's something down here on the track and we're just gonna have to deal with it.' "
Ambrose was third at the start of the final lap.
"The guy [Busch] was sliding across the track, he was gonna spin out and Brad finished him off," Ambrose said. "I'm like, 'Man, there's one, I've got one more to go.' I went up over the hill there and I thought I was gonna hit the fence and kept it off the wall and then we get down to the chicane and I'm like, 'Well, I'm just gonna follow Brad because he'll see the oil before I do and I might be able to save myself,' and I went straight off the track with him.
"That wasn't a good plan, so then I dove to the inside thinking I was gonna get off the oil that way and slid through it through the carousel and then he slid through it afterwards. So then when I got some momentum on him, I gave him a shot there to try and clear him away and we sailed off into Turn 6 and I'm like, 'All I want to do is be offline.' I turned in and slid through the oil and I thought I had blown my chance in Turn 6, and then I got good drive because I went over the curb and I shot back up the inside of Brad and put him on the oil and then he slid on the oil and we snuck through for the win."
2. Kyle Busch deserved to win. Busch was in the wrong place on the track, hitting the oil before everybody else. He led three times for a race-high 43 laps and clearly had the fastest car in the final stint.
What looked like a victory turned into a devastating seventh over the last two laps.
"The 47 [Bobby Labonte] broke and left oil down all over the track," Busch's crew chief Dave Rogers said. "Kyle hit the oil and it allowed the 2 car [Keselowski] to get to us. There is a 100 percent chance it came from somebody else. There is nothing wrong with this M&M's Toyota Camry.
"There was another car [Labonte\ in the field that blew a motor ... and instead of getting off the race track like he should have, he tried to stay out there and run the extra two laps and when he did, he ran right through the groove. That was a mistake by another driver and the rest of us had to deal with it. Kyle was just the first one there."
3. Ford broke a long dry spell. Ambrose's victory was the first for Ford since Greg Biffle's at Texas in April and only the third of the season. Ford had gone 14 straight races without winning despite having Biffle second and Matt Kenseth third in the points.
Ford's win came just in time with Cup headed to Michigan, the manufacturer's backyard, next week. You can bet those on the flight back to Dearborn were both relieved and happy.
4. Jamie McMurray quietly extended his contract with Chip Ganassi Racing. Chip Ganassi doesn't make announcements when he signs drivers to contracts, preferring to keep it private between the team and the driver. Nobody had asked McMurray about his status for next year until the Watkins Glen weekend.
"It's been since May when that all went down," McMurray said. "I haven't really talked about it. Nobody asked me and I didn't really volunteer it. You watch guys the way they handle that. Some like to make it very public and then there are others that just kind of go about their business."
5. Should NASCAR have thrown a caution for the oil on the track? Gordon and Dale Earnhardt Jr. said yes. Ambrose, predictably, said no.
"Oil all over the race track, it's pretty ridiculous they don't want to end a race under caution and put that many cars in jeopardy," Gordon said. "I had no idea there was oil out there. I knew there was all kinds of havoc happening all around."
Earnhardt was more cautious in saying the same thing.
"There was just oil everywhere," Earnhardt said. "You couldn't see it, so you don't know where to run. I saw the leaders coming and I was just trying to get out of the way and they were in oil and I was in oil. It was a bad deal, I think. The track shouldn't have oil on it. But it finished out with all that oil on the track. I don't really like that. It was a bad ugly finish at the end."
Said Ambrose: "I think a big shout out goes to NASCAR. A lot of guys are gonna say, 'Should they have thrown a caution or should they not?' No one wants to see these races finish under caution or bunch back up in these [double-file restarts] and making a random finish. We had the three fastest cars duking it out for the win and that's the way it should be. I think they made the right call."