Hamilton, winner of the last U.S. Grand Prix staged in the United States five years ago, had been second at the start with Alonso lining up seventh.
The Spaniard would have started eighth but Brazilian Felipe Massa took a five-place penalty to move his Ferrari team mate to the clean side of the grid.
"A first-time winner. I'm so happy," beamed Hamilton, interviewed by U.S. Formula One great Mario Andretti on the podium, of picking up where he left at Indianapolis in 2007 by winning the first race at the new Circuit of the Americas.
Image: McLaren Mercedes driver Lewis Hamilton, left, of Britain, sprays champagne after winning the Formula One U.S. Grand Prix auto race at the Circuit of the Americas Sunday, Nov. 18, 2012, in Austin, Texas.