VAISON-LA-ROMAINE, France — With a burst of power on the steep final slopes of the imposing Mont Ventoux, Chris Froome won the 15th stage of the Tour de France on Sunday, re-establishing the dominance that had been predicted for him before the Tour — and that had come into question only days ago.

Froome, the race’s leader, not only sprinted away from the young Colombian climbing sensation Nairo Quintana, but he also gained more than a minute and a half on his two closest rivals for the overall title, Bauke Mollema and Alberto Contador.

“To win the way so many big names have won on this climb is really special to me,” Froome said, calling the stage victory the biggest of his career.

Some cycling watchdogs speculated online that Froome’s stunning final acceleration suggested he might have used performance-enhancing drugs. Froome, of Team Sky, has rejected such suggestions before and did so again Sunday.