David Lebeck, who held the lead after the first and second rounds, shot a 1-over 73 and now is tied for third with Jason Knutzon (64), Jason Buha (66) and Dave Barr (67).
Runge began the third round two shots behind Lebeck and quickly found himself three down after a birdie at one by Lebeck. Three front-nine bogeys brought Lebeck back down to the pack and Runge helped cut the lead with a 12-foot birdie putt at three. He two-putted from 40 feet for another birdie at five and closed his nine with a tap-in at the par-4 9th.
At 13, Runge found water off the tee but saved his par and then kept the solid play going with an eight-foot eagle putt at 14. A pair of three-putts for bogey at two of his last four cost Runge a larger lead.
'I was really happy with the way I played today,' said Runge. 'I didn't hit the ball as well as I did the first two days, but my putting was good and especially my par saves were really key.'
Petrovic erased two front-nine bogeys with three back-nine birdies and a round of 68. He had an opportunity to trim the lead to one, but his birdie putt from 25 feet at 16 lipped out of the hole.
'I am going to just try to play my own game and make birdies and we will see if we can take care of business on Sunday,' Petrovic said.
Lebeck mixed five bogeys and four birdies on Saturday for his 73, but Knutzon posted nine birdies against one bogey.
Casey Martin began the third round in a tie for 11th but struggled to a 2-over 74 on Saturday and trails Runge by 11 shots at 5-under.