Tomasulo stands at 8-under-par 134 with Kevin Johnson and David Branshaw, who both shot 67 in their second rounds at Redwood Meadows Golf and Country Club.
Overnight leader David McKenzie managed just an even-par 71 and is tied for fourth place at 6-under 136 with Keith Nolan, who shot his second straight round of 68.
Tomasulo, who began his round tied for 79th place at plus-2, broke the Redwood Meadows course record by four strokes, not bad for a guy making just his third start on the Nationwide Tour.
'A great round starts creeping into your mind, but you can't think about that,' said the 23-year-old Tomasulo, who has five consecutive top-five finishes on the Canadian Tour, including a victory at the Montreal Open.
'I felt comfortable. I knew I could put something good together.'
Tomasulo began his round on the back nine and opened with consecutive birdies at Nos. 10 and 11 to reach even par. He followed with seven straight pars before really erupting on the front nine.
Beginning at the par-4 first hole, Tomasulo strung together five birdies in a row to reach minus-5. His birdie putts on holes 1-4 averaged more than 15 feet, and he two-putted from 25 feet at the par-5 fifth to end the impressive run.
'These greens are so perfect,' said Tomasulo. 'The hole looked big today, I guess.'
After a par at No. 6, Tomasulo birdied the seventh and then moved to minus-8 by holing a 25-foot bunker shot for an eagle at the eighth. He capped off his spectacular round with a routine par at No. 9 to card an 8-under-par 28 on the front-nine.
'Those are always fun,' Tomasulo said of his round.
Johnson and Branshaw had the day's next best rounds at 4-under-par 67, six strokes behind Tomasulo.
Branshaw's scores ran the gamut, from an eagle at No. 11 to a pair of bogeys, while Johnson's day included six birdies and a double bogey at the par-3 sixth, where he two-putted from 20 feet.
'The green was like a pavement on number six,' said Johnson, a three-time winner on tour who hasn't finished better than fifth this year. 'I hit it great today, but I didn't putt that well.'
Matt Bettencourt (71), Jason Schultz (70) and Erik Compton (68) share sixth place at minus-5. Jeff Gove (69), Dustin White (69), Matt Gallant (70) and Joseph Alfieri (70) are tied for ninth place, one stroke further back.
The cut fell at plus-1 with 76 players failing to move on to the weekend.