The 35-year-old Atwal, involved in a fatal car wreck in March 2007, birdied the final hole for an even-par 72 to match Simpson at 24-under 264 on the Black Creek Club course. Simpson shot a 69, also finishing regulation play with a birdie.
"I've been working for this all my career," said Atwal, the Malaysian Open winner this year on the European tour. "I've had a few things going on away from the course. To finally win in America feels really good and getting my card back on the PGA Tour will be a sweet bonus."
Atwal earned $90,000 to jump from 34th to 15th on the money list with $248,986. The top 25 after the final two events of the season will earn 2009 PGA Tour cards.
"It's good to get back after playing on the tour for four years," said Atwal, who shot a course-record 60 in the second round. "It's the only place I want to play and I feel like I belong."
Prosecutors decided in March not to charge Atwal in the wreck in Windermere, Fla. Witnesses said Atwal and John Park were driving nearly 100 mph in a 45-mph zone when Park failed to negotiate a turn, sending his car airborne into a tree. Florida Highway Patrol investigators had recommended Atwal be charged with vehicular homicide.
The first player from India to earn a PGA Tour card, has eight international wins, including the European tour's 2002 Malaysian Open and 2003 Singapore Masters.
Simpson turned pro in June after finishing his college career at Wake Forest.
"I'm happy," Simpson said. "I wish I could have won. Everything I learned this week will help me next time."
Kris Blanks (68) finished third, four strokes back.