The former Australian V8 Supercar champion backed up his favoritism and superior pace with victory at his 105th attempt in NASCAR's main series, crucially jumping to the lead on the final restart with two laps remaining after Kyle Busch locked up his brakes entering Turn 1.
From third on the gridm Ambrose was quickly putting the pressure on his Richard Petty Motorsports team-mate AJ Allmendinger, taking the lead for the first time on lap nine after Kurt Busch, running a lap down after an early spin, pushed Allmendinger under braking for the inner loop forcing him off the track.
Once ahead, the Australian had the pace to keep his rivals at bay, although his three-stop strategy would put him in traffic between those initially attempting a two-stopper. However, he kept his nose clean while charging through the field, eventually arriving on Kyle Busch's rear bumper as the lap-count faded.
When the fourth caution waved for an incident involving Brickyard 400 winner Paul Menard, Ambrose got his best chance to overtake his Joe Gibbs Racing rival, although Busch's complicity made it a bit easier for him.
However, he had to dispose first of Penske's impressive Brad Keselowski, who actually came out leading of turn one following the last restart. Ambrose quickly put a move on him out of the inner loop, bumping him entering turn five to claim the lead for good.
As Ambrose pulled away mayhem unfolded on the final lap, first with a massive crash involving Roush Fenway's David Ragan, road-course specialist Boris Said and Michael Waltrip Racing's David Reutimann - the latter flipping spectacularly at turn two after tangling with Ragan's already stricken Ford.
The race had to be called under caution following the wreck and also a second one that unfolded when Tony Stewart missed the inner loop and lost control of his car causing further chaos.
Ambrose's victory adds to his tally at Watkins Glen, where he won three out of four races entered in the NASCAR Nationwide Series, this year ironically missing the event due to lack of sponsorship.
He becomes the fourth foreign born driver to win a Cup event, following on the footsteps of Canadian Earl Ross, Italian-born Marco Andretti and Colombia's Juan Pablo Montoya.
"I've sacrificed so much to get here and to finally win and be here in Victory Lane in the Cup Series is a dream come true," said a jubilant Ambrose. "I flew the kids home yesterday. It was the little one's first day at school. I was desperate to be there for her and this kind of makes up for it...
"Winning in the Cup Series for Stanley is just an incredible feeling and I'm very, very proud."
Keselowski, whose road-course experience is among the most limited for Cup regulars, impressed with second place a week after his Pocono win placed him in solid contention for a wild-card Chase berth. The Penske driver led the race for two laps early into the second half, passing Kyle Busch and comfortably keeping him at bay.
A two-stop strategy mirroring Busch's coupled with his revealing pace, placed him in contention for victory and despite missing on a possible third win this season, he didn't feel sorry at all for losing out to Ambrose in the end.
"I wanted to win, but if I'm going to lose on a road course to someone, Marcos Ambrose is the man," said Keselowski, now 14th in points. "He's so good on restarts and I thought we had a shot at it and that's all you can ask for as a driver.
"We were really good on long runs today. I'm proud of the day. I'm proud of the finish. It was a good points day for us."
Busch was a disappointed third but his result vaults him up to the points' lead, one that he may well eventually inherit through his three wins once the Chase berths are set in four-weeks' time when bonus for wins come into play.
"Just knew exactly what not to do and did it anyway," rued Busch about his restart mistake into turn 1. "Just got in there and I didn't think I got in there too fast, but the car just didn't slow down the way I needed it to and then it didn't turn the way I needed it to.
"Saw sprinkles on the windshield, but everybody else made it fine through there. I just screwed up!"
Michael Waltrip Racing's Martin Truex was a impressive fifth, followed by an equally surprising Joey Logano, who rounded out a busy weekend as he ran his third race in three days, competing in the Nationwide and Grand Am events on Saturday.
Earnhardt Ganassi's Montoya ran on the same strategy as Ambrose and looked a challenger for victory but reported a suspension problem to his team on the radio in the closing stages of the race, finishing seventh after contending for third out of the first turn on the last restart.
Both Ragan and Reutimann were unharmed in their incidents, as where Penske's Kurt Busch and JGR's Denny Hamlin, both of whom crashed heavily with suspected brake issues, Hamlin hitting head on against the barriers at Turn 1.
Pos Driver Car Laps 1. Marcos Ambrose Ford 92 2. Brad Keselowski Dodge 92 3. Kyle Busch Toyota 92 4. Martin Truex Jr. Toyota 92 5. Joey Logano Toyota 92 6. Kevin Harvick Chevrolet 92 7. J.P.Montoya Chevrolet 92 8. A.J.Allmendinger Ford 92 9. Jeff Burton Chevrolet 92 10. Jimmie Johnson Chevrolet 92 11. Clint Bowyer Chevrolet 92 12. Carl Edwards Ford 92 13. Jeff Gordon Chevrolet 92 14. Matt Kenseth Ford 92 15. D.Earnhardt Jr. Chevrolet 92 16. Ryan Newman Chevrolet 92 17. Jamie McMurray Chevrolet 92 18. Brian Vickers Toyota 92 19. Bobby Labonte Toyota 92 20. Casey Mears Toyota 92 21. Andy Lally Ford 92 22. Boris Said Chevrolet 92 23. Regan Smith Chevrolet 92 24. Robby Gordon Dodge 92 25. Mark Martin Chevrolet 92 26. Kasey Kahne Toyota 92 27. Tony Stewart Chevrolet 92 28. David Ragan Ford 91 29. David Reutimann Toyota 91 30. Ron Fellows Chevrolet 91 31. Greg Biffle Ford 91 32. Paul Menard Chevrolet 85 33. David Gilliland Ford 79 34. Terry Labonte Ford 78 35. Andrew Ranger Ford 75 36. Denny Hamlin Toyota 65 37. T.J. Bell Chevrolet 58 38. Kurt Busch Dodge 48 39. Scott Speed Ford 45 40. Joe Nemechek Toyota 12 41. Michael McDowell Toyota 7 42. J.J. Yeley Ford 5 43. Mike Skinner Toyota 4
