Audi trio Loic Duval, Allan McNish and Tom Kristensen claimed victory at Austin to extend their World Endurance Championship lead.
The #2 Audi R18 e-tron quattro triumphed by 23 seconds over the second-placed Toyota TS030 HYBRID shared by Sebastien Buemi, Stephane Sarrazin and Anthony Davidson.
The Audi was the quicker car, but the Toyota's ability to double stint its Michelin tyres and its better fuel consumption kept Buemi and his team-mates in the fight until the closing stages.
McNish said: "It was a surprise to be honest. They could double stint their tyre when we couldn't.
"The car was fantastic: the guys set it up extremely well given the lack of practice time. We are very, very pleased."
The second Audi, shared by Marcel Fassler, Andre Lotterer and Benoit Treluyer finished third, two laps down on the sister car.
The car lost time when Fassler was forced off line lapping a GTE Pro class Porsche in the opening hour, putting him over one of the pyramid kerbs designed to prevent corner cutting.
He was then hit up the rear, which damaged the rear bodywork. That forced an unscheduled pitstop and trip into the garage for repairs.
Lotterer subsequently lost more time when a fuse fell out, almost certainly as a result of the earlier incident.
The result means that Audi has won the WEC manufactuers' title, presuming that Toyota does not run a second car in each of the final three races, for a second season in a row.
Duval, McNish and Kristensen now lead the drivers' standings by 33 points, which means they will win the world championship even if they finish second to their team-mates in each of the remaining three races.
The LMP2 division was won for a second race in a row by the G-Drive/Delta-ADR ORECA-Nissan 03 driven by John Martin, Roman Rusinov and Mike Conway.
They ended up a lap clear of their nearest rival, the Pecom/AF ORECA-Nissan, after its two closest challengers ran into problems.
The two OAK Morgan-Nissan LMP2s had run ahead of the winning G-Drive car during the second stint, but a collision between Ricardo Gonzalez and David Heinemeier Hansson resulted in stays in the pits to repair suspension damage for both cars.
Second place for the Pecom trio of Pierre Kaffer, Luis Perez Companc and Nicolas Minassian was enough to move them to within three points of LMP2 drivers' leaders, Gonzalez, Bertrand Baguette and Martin Plowman, who finished seventh in class after their delays.
ASTON DOMINATES GT CLASSES
Aston Martin Racing claimed GTE Pro honours with the Vantage driven by Frederic Makowiecki and Bruno Senna.
They were in charge of the class for the full race duration and ended up winning by 15s over Gianmaria Bruni and Giancarlo Fisichella in the best of the AF Corse Ferrari 458 Italias.
Makowiecki enjoyed a lead of just over a minute until the closing stages when he took a splash-and-dash fuel stop.
Jamie Campbell-Walter and Stuart Hall edged a close internecine Aston Martin GTE Am battle. Campbell-Walter overtook Kristian Poulsen, who shared with Nicki Thiim and Christopher Nygaard, to take the victory in the final 15 minutes.
Results - 187 laps: Pos Cl Drivers Team/Car Time/Gap 1. P1 Kristensen/Duval/McNish Audi 6h00m31.331s 2. P1 Davidson/Buemi/Sarrazin Toyota +23.617s 3. P1 Lotterer/Treluyer/Fassler Audi +1 lap 4. P1 Prost/Heidfeld/Beche Rebellion Lola-Toyota +4 laps 5. P2 Rusinov/Martin/Conway Delta-ADR ORECA-Nissan +9 laps 6. P2 Perez Companc/Minassian.Kaffer Pecom ORECA-Nissan +10 laps 7. P2 Holzer/Kraihamer/Charouz Lotus +13 laps 8. P2 Graves/Walker/Junco Delta-ADR ORECA-Nissan +14 laps 9. P2 Zugel/Dyson/Kimber-Smith Greaves Zytek-Nissan +15 laps 10. P2 Pla/Heinemeier Hansson/Brundle OAK Morgan-Nissan +15 laps 11. P2 Baguette/Gonzalez/Plowman OAK Morgan-Nissan +17 laps 12. GTE P Senna/Makowiecki Aston Martin +20 laps 13. GTE P Bruni/Fisichella AF Ferrari +20 laps 14. GTE P Kobayashi/Vilander AF Ferrari +20 laps 15. GTE P Lieb/Lietz Manthey Porsche +20 laps 16. GTE A Hall/Campbell-Walter Aston Martin +22 laps 17. GTE A Nygaard/Poulsen/Thiim Aston Martin +22 laps 18. GTE A Narac/Vernay Imsa Porsche +22 laps 19. GTE A Potolicchio/Aguas/Malucelli 8Star Ferrari +23 laps 20. GTE P Bergmeister/Pilet Manthey Porsche +24 laps 21. GTE A Ried/Roda/Ruberti Proton Porsche +24 laps 22. GTE A Bornhauser/Canal/Rees Larbre Corvette +24 laps 23. GTE A Gerber/Griffin/Cioci AF Ferrari +25 laps 24. GTE A Krohn/Jonsson/Mediani Krohn Ferrari +31 laps 25. P2 Nicolet/Merlin/Maris OAK Morgan-Nissan +39 laps Retirements: GTE P Mucke/Turner/Gavin Aston Martin 118 laps GTE P Dalla Lana/Lamy/Stanaway Aston Martin 84 laps P2 Weeda/Liuzzi/Rossiter Lotus 0 laps