Italian Manassero rebounded from a three-putt bogey on the par-4 17th with a birdie on the par-5 18th to get to 14-under 196 on the North Course at TPC Toronto at Osprey Valley on Saturday.
Trying to win for the first time on the PGA Tour, the 32-year-old has eight international victories.
"I missed the short one on 17, and I did miss a couple more short ones today," Manassero said.
"I try to get a good attitude, a good thought process, talk well to myself. Very basic things.
"I've matured a lot and I have a better perspective towards, for example, a day like tomorrow."
Fox also birdied the 18th.Â
The 38-year-old New Zealander won the Myrtle Beach Classic last month in a playoff for his first PGA Tour title.
"To be honest, everything went pretty right," Fox said.
"I drove it great. I think if you do that round here, you give yourself lots of chances. Had a lot of good wedge shots, holed a few putts early. Just played really solid kind of stress-free golf for the most part."
Lee Hodges, Kevin Yu and Matt McCarty were a stroke back. Hodges and Yu shot 63, and McCarty had a 64.
Mackenzie Hughes (64) was 12 under with Jake Knapp (66) and Andrew Putnam (68).
With 15 golfers within three strokes of the lead, the possibilities appear endless.
"It's anyone's game at this point," Canadian Hughes said.
"No one has been able to totally light this place on fire yet."
Nick Taylor, the 2023 winner at Oakville, eagled the 18th for a 69 to get to 10 under. Countrymen Adam Hadwin (65) and Taylor Pendrith (67) also were 10 under.
Masters champion Rory McIlroy missed the cut on Friday, following an opening 71 with a 78, as did Aussie trio Harryson Endycott, Aaron Baddeley and Karl Vilips.
With AAP.
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