O'Hair, the third-round leader, was two behind Mickelson heading to the 17th. However, he dumped two balls into the water to tumble down the leaderboard and secure the Players Championship title for Mickelson.
Lefty closed with a three-under 69 to hold off Sergio Garcia, who birdied four of the last five holes to shoot 66 and finish two back.
As usual, there is a stellar field headed to the TPC Sawgrass this week. World No. 1 Tiger Woods continues his rehab from knee surgery, but 24 of the top-25 and 45 of the top-50 players in the world will be on hand this week.
The field includes 44 of the last 45 tournament winners on the PGA TOUR as well as 24 major champions. It will also be a diverse field with 55 of the 144 players coming from outside the United States.
U.S. Presidents Cup captain Fred Couples, the 1984 and 1996 winner, got into the field late as Will Mackenzie backed out while recovering from knee surgery. Couples will tee it up at Sawgrass for the 25th time.
The GOLF CHANNEL will have six hours of coverage each of the first two days, while NBC takes over for the weekend and will have five hours of action each day.
The PGA TOUR heads back to Georgia next week for the AT&T Classic. Zach Johnson downed Ryuji Imada in a playoff for the title last year, his second win at the event and third in the state of Georgia.