Johnson, of Columbia, S.C., birdied the final two holes and closed with a 3-under-par 69 for 9-under 279. Allenby, who parred the last two holes, carded a 70.

"It's kind of hard to explain," said Johnson, who earned $1.08 million. "I haven't quite grasped everything yet. Right now I'm feeling pretty good and I'm obviously very, very excited."

Allenby has not won since 2001.

Charles Howell III, a co-leader with Tag Ridings beginning the round, shot a 73 and tied for third place at 7-under 281 with Robert Garrigus (69), Steve Allan (69), Woody Austin (69), Ryuji Imada (69), Matthew Goggin (69) and Davis Love III (70).

Ridings fell to a tie for 27th place after a 7-over 79.