Danny Ellis carded a 1-under 71 to finish alone in second place at 18-under-par 414 while Michael Allen was one shot further back at 17-under-par 415. John Riegger and David Branshaw shared fourth place at 15-under-par 417.
The players battled through 108 holes over six days at Orange County National and in the end it was Gronberg who finished as the top dog and will now enjoy his rookie season on the PGA Tour in 2004.
Gronberg was one shot behind Ellis to start the day at the Panther Lake course and picked up his first birdie at the par-5 second. He struggled with a bogey at the very next hole but managed to recover with back-to-back birdies starting at the par-5 seventh.
The Swede faltered with a bogey at the ninth but put together a strong finish to earn medalist honors.
In addition to exempt status on the PGA Tour next year, Gronberg walked away with a $50,000 first place check.
Gronberg tallied a birdie at the par-4 13th before picking up another birdie at the par-3 15th. The 33-year-old then made it two in a row with a birdie at the par-4 16th.
'There's no guarantee that I will do well next year,' said Gronberg. 'But I feel very good. This is a nice reward. I would have taken any position top-30 and ties before the week came.'
Fellow Swede Daniel Chopra finished alone in sixth place at 13-under-par 419. Omar Uresti, Kris Cox, Arjun Atwal, John Maginnes and Wes Short followed at 12-under-par 420.
'It's got to be one of the best rounds I've ever played,' said Uresti, who closed with a 64 to vault from a tie for 34th to a share of seventh. 'This one means a whole lot more. It's the first time in a long time I've been able to throw up a really low number in a final round when it meant something.'
Tjaart van der Walt, Brian Bateman, Ken Duke and Dan Olsen tied for 12th place at 11-under-par 421 to earn playing privileges on the PGA Tour next year. Kevin Muncrief, Russ Cochran, Todd Hamilton, Brian Kortan and Hunter Mahan were one shot further back and also advanced at 10-under-par 422.
Steve Pate will make his return to the PGA Tour. Pate shot a 68 on Monday to join Rich Barcelo, Scott Hend, Kevin Na and Roger Tambellini at 9-under-par 423. Trevor Dodds and Boyd Summerhays followed at 8-under-par 424.
Brian Gay, Deane Pappas, Roland Thatcher, Grant Waite, Hirofumi Miyase, Danny Briggs and Jay Delsing finished at 7-under-par 425 to round out the list of those advancing to the PGA Tour in 2004.
The next group of 50 or so players earn exempt status on the Nationwide Tour in 2004. That group includes D.J. Trahan, Gavin Coles and Greg Chalmers.