Ambrose had his first Sprint Cup Series victory in sight Sunday when a caution with nine laps remaining delayed what seemed to be an inevitable win. But as he tried to conserve fuel by turning his motor on and off under the yellow, his car stalled and six cars passed him on the track.
NASCAR ruled Ambrose failed to maintain pace and ordered him back to seventh position when the race restarted with five laps left.
That made it easy for Johnson, the four-time defending series champion, to coast to a coveted road course win.
Ambrose had to settle for sixth.
