DiMarco, who shot a final-round 7-under 65, earned his first victory of the season to go along with $612,000.
Look at the field, DiMarco said in reference to Duval, Vijay Singh and Davis Love III. When I won last year (at the Pennsylvania Classic), I beat some good players but not the big names. To do it against the big names is very special.
This was the only thing missing from my year.
Duval put forth a valiant effort in trying to successfully defend his title, carding seven birdies and an eagle on Sunday. He then went to a television booth overlooking 18, where he watched DiMarco sink a 15-foot birdie putt to tie him at 21-under 267.
I was expecting to be in a playoff, Duval said. I didnt want to be in a playoff, but I was expecting it.
In the extra session, Duval sailed the green with a 9-iron approach shot from 132 yards. His ball landed in the grass above the lip of the back bunker.
Unfortunately, where the ball went left me with a difficult, difficult shot, Duval said. I almost laughed about it.
Duval was able to pitch his ball eight feet left of the hole, but was unable to convert the par save.
I played great. I played well enough to win, Duval said. After hitting so many good shots and then to have that happen to me, theres nothing you can do but laugh. Its kind of unbelievable.
Duval started the day six shots back of overnight leader Joel Edwards. Edwards led by a single stroke over Love, but faltered in the final round with a 2-over 74. He tied for 7th.
Love managed to birdie the 2nd and 3rd holes Sunday to take a two-shot lead at 19-under; though, he bogeyed the par-3 8th and parred his final ten holes to shoot 71 and finish in solo fifth place.
It marked the sixth time this year that Love has played in the final group on Sunday and failed to produce victory.
This was the final event before the $5 million Tour Championship, which takes the top 30 in earnings.
Jesper Parnevik started the week $676 behind No. 30 on the money list, Kenny Perry. The Swede led Perry by four shots entering the final round, but struggled to a 71. Meanwhile, Perry closed in 66 to earn a trip to the Champions Club in Houston, Tx.
Really, I was not nervous, Perry said. I figured I had everything to gain and nothing to lose.
There is now just one tournament remaing (Southern Farm Bureau Classic) for players to finish inside the top 125 on the money list and secure their tour cards for next season.
Per-Ulrik Johansson and Neal Lancaster accomplished that this week.
Lancaster was 118th on the money list before finishing tied for third, while Johansson moved from 122nd to 97th thanks to a tie for seventh.
Full-field scores from the Buick Challenge