Don Pooley and Joe Daley each posted rounds of 6-under 66 and share second at minus 15.
Thunderstorms once again pounded the Fox Den Country Club, causing a suspension of 2 1/2 hours late in round three. All players completed their rounds and the final 18 is on schedule for Sunday.
Slocum is on a phenomenal run in the past three weeks, having won the Greater Cleveland Open two weeks ago and placing third last week at the Dayton Open.
During the stretch, Slocum broke Clark Dennis' bogey-free streak of 98 holes. He reached 106, but three-putted from eight feet at the seventh hole in Friday's second round.
'I don't know what's going on these days,' said Slocum, who has missed only four greens and five fairways in this tournament. 'I'm just along for the ride.'
Slocum birdied four of his first six holes Saturday to establish himself as the man to catch. He two-putted from 45 feet for a birdie at the par-5 10th and holed an 18-foot birdie putt at 12 to get three shots clear of the field at 18-under-par.
Slocum putted out on 15, then thunderstorms caused the delay in the round.
'As soon as the horn blows, I try to relax as much as possible,' said Slocum. 'The stopping and starting always affects you. I try to start back and get warmed up and focused when they tell us it's time.'
After play resumed, Slocum played a 4-iron onto the 216-yard 16th green but two-putted for par. He added another par at 17 and drained a three-foot birdie at 18 to move ahead by four.
'I feel like the ball is in my court,' said Slocum, who can become the tour's first two-time winner in 2001. 'If you're in the lead, you're obviously playing well. If I go play a good, solid round, somebody has to play very well to catch me. I'm not going to change anything for tomorrow, and hopefully it will be good enough.'