The American, who won the US PGA Championship this summer, saw off compatriot Jordan Spieth to win by three shots and give himself a chance of lifting the Fed Ex Cup.
Sharing the overnight lead with the Australian Marc Leishman, Thomas was well placed.
After two rounds of 71 and 67, a third round score of 63 put him firmly in the mix.
With conditions dry, it enabled lower than expected scores on the front nine.
Three birdies and an eagle from Thomas on the front nine on the final day gave him control.
Thomas said it was the first time he had won without having his "best stuff" and downplayed any notion that his victory would reverberate around the tour.