Tomasulo, a one-time winner on the Nationwide and Canadian Tours, was through 36 holes at 5-under 137 for a one-shot lead on two players. He missed an opportunity to stretch his lead to two shots when he left a short birdie putt on the edge of the hole at the 18th.
'I didn't get committed to the line,' said Tomasulo.
Brendon Todd (69) and Rich Barcelo (70) were tied for second place at 4- under 138, with 10 players knotted another shot further back at 3-under 139.
Four players who didn't fare well on Friday were the first-round co-leaders.
Bill Lunde (72), Kelly Grunewald (73), Bryce Molder (75) and Dave Schultz (75) all posted rounds over-par after sharing a one-shot lead overnight. Only Lunde and Grunewald were within three strokes of the new leader.
Tomasulo started with a bogey on the first hole after three-putting from 60 feet. But he rebounded with a birdie on No. 2 after knocking a 7-iron to about 10 feet.
Four consecutive pars were followed by a gap-wedge to 10 feet for birdie at No. 7, then three more pars. Tomasulo made back-to-back birdies at the 11th and 12th, both on three-foot putts, then rolled in a 19-footer for birdie at the 15th.
His missed birdie opportunity at the 18th came after a good approach shot to five feet.
'That was probably my best iron shot all day, actually,' said Tomasulo. 'I had a good number to get aggressive with the wind ... I hit it in there like five feet, and just didn't really get comfortable with the putt. It looked like it could have been inside left edge, outside left edge and I hit it on the edge and just lost speed a little bit.'
Tomasulo's only Nationwide Tour victory came at the 2005 Alberta Classic, where he won playing on a sponsor's exemption in his first year out of college.
Now 26, Tomasulo believes his game is in good enough shape to produce another win.
'[The] last two seasons have been a bit frustrating, but my game feels like it's really progressing this year,' he said. 'It feels better than it ever has, and feel like I'm really playing solid right now, smart golf, and taking my chances when I can and going at pins when I can.'
Defending champion Daniel Summerhays, who became the first-ever amateur to win on the Nationwide Tour when he claimed this event last year, missed the cut by a shot at 4-over 146. Summerhays shot a 72 on Friday.