Bob Conrad shot a 64 to finish alone in second at 11-under 129 while Mario Tiziani, Andrew Sanders, Mark Johnson and Jason Enloe were tied at 10-under 130.
Duke, the 1999 Order of Merit champion, spoke to his father over the phone Thursday night seeking advice on how to correct his swing. The 33-year-old saw a difference Friday, with a bogey-free round that included a stretch of three consecutive birdies from the second and an eagle at the par-5 10th.
'We went over a few things on the phone and out on the range this morning, I just knew it was one of those days,' said Duke. 'Everything felt so much better. You just hope you can carry it on the course with you.'
Conrad was at 5-under to begin the round and went on a roller coaster ride to jump into second. His round featured seven birdies, two eagles, three bogeys and a double-bogey.
'I made a few mistakes, but that happens,' said Conrad. 'In this weather, it will be a free-for-all this weekend. I'll just go out, try and eliminate those mistakes and see what happens.'
The weather was perfect as scoring soared. Danny Paniccia had the low round of the day with an 8-under 62 to jump into a tie for seventh with seven others, including Texas Challenge winner Hank Kuehne.
The cut fell at 4-under 136, a new record for lowest 36-hole total on the Canadian Tour. Jeff Quinney, who won the first leg of the Scottsdale Swing last week at McCormick Ranch, fell on the cut line. He is among 65 players who survived to play the weekend.
Full-field scores from the Scottsdale Swing at Eagle Mountain