Haas matched the tournament record at 21 under at Hillcrest Country Club and earned $130,500 to jump from 12th to fourth on the money list with $331,766, guaranteeing his return to the PGA Tour next year as a top-25 finisher on the money list.
"It's awesome," said Haas, the Price Cutter Charity Championship winner last month in Springfield, Mo., "I had a pretty slow start to the season, but once I got the engines revved up, I've been going pretty good. I'm going to be confident for the rest of the year and hopefully I can take that into the next season."
The 33-year-old former Oklahoma player also is a victory away from an immediate tour promotion.
Haas entered the final round three strokes behind Summerhays after rounds of 68, 64 and 67.
Summerhays finished with a 68. The former BYU player birdied Nos. 2-4, then parred the final 14 holes.
"I felt like I played my best golf today. I really did," Summerhays said. "I drove it the best I drove it all week, hit a lot of good wedge shots and I skimmed the edges on probably four or five putts. One of these Sundays is going to be mine."