The Englishman shot 2-under 70 to finish the week at Doral at 16 under par.
Watson, the 54-hole leader, shot 74 to close.He He missed a 12-footer for birdie on the final hole that would have forced a playoff.
Rory McIlroy shot 67 on Sunday to finish alone in third, three back of Rose.
Keegan Bradley, who held the lead for a stretch on Sunday, struggled on the final nine to finish in a tie for eighth.
The win marks the third consecutive year Rose has won on the PGA Tour.