Spike McRoy, an overnight co-leader, had to eagle the last to catch Matteson in the clubhouse. He only managed par and a round of even-par 71 to share second with Johnson Wagner (67) and Mathew Goggin (68) at minus-11.
Kevin Gessino-Kraft fired a 6-under 65 and finished alone in fifth place at 10-under-par 274 at Empire Lakes Golf Club.
Matteson began the final round two behind and wasted little time in making up the deficit. He drained a 25-foot birdie putt at the first and followed it up with a 12-footer for birdie at the second.
Matteson added another birdie at the par-5 fifth and tapped in a short birdie putt at No. 8. At this point, he was one ahead of McRoy, but the 2002 B.C. Open winner found trouble at the par-3 ninth.
McRoy's tee ball landed in the water, and after his drop, his third found the front, greenside bunker. He made double bogey, but atoned for the mistake with birdies at 10 and 12 to get within one at minus-12.
Matteson made some solid pars down the stretch, including a 6-footer at 13 and a 4-footer at the 14th. He pulled the wrong club at the par-3 17th and came up short and right of the green. Matteson chipped to 2 feet and rolled in the par save.
He had 15 feet for birdie at the last, but missed the chance to pad his lead. Matteson would watch McRoy come into the clubhouse to see if a playoff would be needed.
McRoy missed the green at the 15th and ran his chip 25 feet past the hole. He could not save par and fell two back. McRoy parred 16 and 17 so he would need eagle at the last to match Matteson at minus-13. McRoy drove into the right rough and laid up and when his wedge approach missed the hole, Matteson won the title.
'I played really well on the front side, made some birdies early and struggled through the back,' said Matteson, who pocketed $81,000 to extend his lead on the money list. 'Today I was very lucky that I made all of my par putts on the back side.'
Matteson has some goals for the remaining 2005 schedule. One more win (he also captured the Virginia Beach Open), and he earns a 'battlefield promotion' to the PGA Tour. He is also about $50,000 away from Zach Johnson's 2003 all-time money record on the Nationwide Tour.
'I think we'd like to get the all-time money lead,' said Matteson. 'If we got another win, that'd be great, but I'm looking to have a good season the rest of the year.'
Danny Ellis (67), John Mallinger (70) and David Branshaw (71) tied for sixth place at 9-under-par 275.
Jason Caron, who shared the lead with McRoy after Saturday's third round, struggled to a 3-over 74 and shared ninth place with Tom Scherrer (69), Keith Huber (69), Tom Johnson (69), Robin Byrd (70), Jeff Klauk (73) and Tom Carter (73). The group came in at minus-8.