Rory McIlroy charged into contention but American Wyndham Clark fired a level par 70 to maintain a one-stroke lead after Friday's second round of the US PGA Tour's Canadian Open.
World number 293 Clark, who led by one stroke after day one, made bogeys on two of the last four holes to stand on seven-under 133 after 36 holes at St George's Golf and Country Club in suburban Toronto.
"Overall I played really good. I felt really confident with my game," Clark said. "I had some little mishaps coming in, but other than that I played some great golf for 36 holes. If I do that again, I'll have a great chance come Sunday."
Northern Ireland's eighth-ranked McIlroy –- the 2019 winner and defending champion after Covid-19 caused a two-year hiatus -- birdied two of the last four holes to shoot 68 and share second on 134 with England's Matthew Fitzpatrick and Americans Keith Mitchell, Jim Knous and Alex Smalley.
Four-time major winner McIlroy sank an eight-foot birdie putt at the par-5 15th and rolled in a 23-foot birdie putt at 17 before parring the last with a clutch four-foot putt.
"Overall it was a good score," McIlroy said. "I scrambled well when I needed to. I didn't really take advantage of how well I hit it off the tee. But overall I felt a couple under was a fair reflection of how the day went."
Fitzpatrick, ranked 17th, led by two but made double bogey at the 14th and bogeys on the last three holes.
"Just didn't hole the putts I needed to on the last three," Fitzpatrick said. "Just pathetic. Yeah, just pathetic finish really with the putter.
"Disappointing finish, but definitely not out of it."
The seven-time DP World Tour winner seeks her first PGA victory after sharing fifth at last month's PGA Championship for his best major finish.
Clark, 28, chases his first US PGA victory as well, his best finish a runner-up effort at the 2020 Bermuda Championship.
Clark hit only eight greens in regulation, but backed his "great" short game and putting.
- 'Pretty awesome' finish -
Fitzpatrick reeled off three birdies in a row thanks to five-foot putts at the par-5 ninth and par-5 11th sandwiched around a 15-footer at the par-4 10th, reaching 10-under par.
But Fitzpatrick needed four shots to reach the fringe at the par-4 14th on the way to a double bogey, then followed an 11-foot birdie putt at the par-5 15th with three bogeys.
His troubles left the lead to Clark, who made birdie putts from just inside five feet at the par-3 eighth and 11, but missed the green at 12 and made his first bogey of the week.
Clark knocked in a nine-footer from the fringe to birdie the par-4 14th, but then fell back with back-to-back bogeys, sinking a nine-foot bogey putt at 15 but missing a par putt half as long at the par-3 16th.
At 18, Clark had a "semi-plugged" bunker lie but popped out to four feet and saved par to keep the lead.
"I would love to say I was trying to do what I did," Clark said. "It was definitely the best save I've had of the year. It was pretty awesome."