Atwal, who was in the running for a top-10 after two days finished the week with a total of 12-under 272.
In sharp contrast to his sedate round of one-under 70 with 17 pars and one birdie on the third day, Atwal shot five birdies but also gave away three bogeys for a 69.
He birdied second and fourth, dropped a shot on fifth, before a birdie on eighth and bogey on ninth saw him end the front nine in 34.
On the back nine, he birdied the 12th, bogeyed the 15th and again landed a birdie on 17th to close in two-under.
Steve Stricker nailed a 25-foot putt off the 18th green to win the John Deere Classic for the third straight year.
Stricker, who led by five strokes when he made the turn, fell behind rookie Kyle Stanley by two shots on the back nine, and then birdied the final two holes to close with a 2-under 69.
Stricker became only the 10th golfer since World War II to win a tournament three straight times. He finished at 22-under 262 to beat Stanley by one stroke and move to second in the FedExCup standings.
Matt McQuinlan who had missed the cut in his previous 10 tournaments, shot a 64 to tie Zach Johnson (65) for third at 17 under. Charles Howell III (64) and Chez Reavie (72) were another stroke back.