Darren Griff posted his second 69 in as many days and is tied for second place at minus-6 with Lee Williamson. Williamson carded a 2-under 70 Saturday.
Chad Spencer (71), Jon Turcott (68) and Josh Habig (71) are tied for fourth place at 5-under-par 138.
Hartwick chipped in for birdie on the 10th, his first. He collected another birdie on the 13th at Hazelmere Golf Club.
Around the turn, Hartwick birdied the par-five seventh to climb to 8 under, but a bogey on the ninth, his last, meant Hartwick's lead was one instead of two entering round three.
'It was an up and down day. My ball striking wasn't as good as Thursday, but I had a good short game,' Hartwick admitted. 'It was a little rough, but I managed to hang in there. I think the course was playing a lot tougher today. It's a hard enough layout, but there were some tricky pin placements and that wind just added to it.'
Andy Doeden (72), Steve Friesen (70), Brian Guetz (73), Clint Jensen (70), Eric Jorgensen (71) and Jim Lemon (72) are tied for seventh place at 4-under-par 140. Wes Heffernan and James Lepp, who was the first Canadian to win the NCAA Individual Championship, are one stroke further back at minus-2.
'I had it going the wrong way for most of the day,' said Lepp, who is making his professional debut this week. 'But holing out on nine was a great way to end it. I don't know if I was leaking oil or not, but I just couldn't get anything to fall.'
The cut line fell at 2-over-par 146 with 63 players moving on to the final two rounds.