OAKLAND, Calif. — Dallas kept its playoff hopes alive by the slimmest of margins after Dak Prescott converted a fourth-down sneak by the width of an index card to set up Dan Bailey’s go-ahead 19-yard field goal, and Derek Carr fumbled the ball inches from the goal line with 31 seconds left to give the Cowboys a 20-17 victory over the Oakland Raiders on Sunday night. The first key play came when Cowboys coach Jason Garrett decided to go for it on fourth-and-1 from his own 39 with about five minutes left in a tie game.