She nearly holed her approach shot on the opening hole before settling for par. The eagle she barely missed out on would come four holes later.
Five birdies followed in her bogey-free round, vaulting Matthew into top spot at 15-under-par 127 at the tournament's midway point.
"It feels really good, I've holed a lot of putts but I've given myself a lot of chances," Matthew said. "I wouldn't really say I've holed many super-long ones but just every time I've given myself a chance I'm kind of taking advantage of them."
The 127 total blew away her previous career-best 36-hole mark on tour by five strokes.
Matthew was three shots ahead of American Angela Stanford (67). Anna Nordqvist of Sweden shot a 64 and was tied at 11 under with American Ryann O'Toole (65), Spain's Belen Mozo (66) and South Korea's Chella Choi (65) and Meena Lee (66).
Matthew, who hit a 25-foot-putt for eagle on the par-5 fifth hole, birdied two of the next three holes for a 32 on the front nine. She was at a loss to explain her comfort level on the southwestern Ontario course.
"I would say first time here, obviously suits my eye a little bit, maybe just got the speed of the greens," Matthew said. "I think that's the important thing. When you're holing putts, it all seems quite easy."
Matthew missed only one fairway on the day and hit all but one green in regulation.
It was warm and sunny Friday but the greens were still moist from rain earlier in the week. Stanford played this event in its inaugural season last year and said the course is playing much different this time around.
"I think the firmness of the greens last year made it a little bit tougher," she said. "You had to kind of pay attention to where you were landing it.
"This week they're so soft you can kind of go pin hunting."
The wide fairways and open layout of the 6,330-yard, par-71 course rewarded consistency off the tee. The ball often sat tight near the pin after quality approach shots instead of rolling through, resulting in many birdie and eagle opportunities.
Eleven players cracked the double-digit mark after only 36 holes. It could mean a score of -20 — or better — will be needed to win the US$1.3-million tournament.
Top-ranked Inbee Park of South Korea, who is looking to win her fourth straight LPGA Tour event, had a 67 and was tied with three other players at 10 under. Brooke Henderson of Smiths Falls, Ont., shot a 66 and was the top Canadian at 6 under.
The weather forecast is calling for the same comfortable conditions over the last two rounds.
"Course conditions determine a lot. This setup, like last year, was not easy," Stanford said. "Anywhere in the world if greens get soft, it makes it a lot more accessible. So I don't think the layout is what makes it easy. I think just the fact that they've had so much rain here and it's softer.
"But if it's firm and fast, then you've got to pay attention to where you land your ball and running through fairways. So I think it's just the greens being soft has been our gift this week."
Park is trying to become the first golfer to win four straight LPGA tournaments since Lorena Ochoa in 2008.
"I mean this golf course is very scorable, and a lot of people are going on birdie streaks," Park said. "It's tough to follow that many birdies all four days. I'm trying my best to get it out there."
Nancy Lopez holds the tour record with five consecutive victories in 1978, a mark equalled by Annika Sorenstam over the 2004-05 seasons.
Park recently won the U.S. Women's Open to become the first player to win the year's first three majors since Babe Zaharias swept the three majors played in the LPGA's inaugural season in 1950. Park will go for her fourth major in a row at the Women's British Open next month.
Notes: Matthew has recorded 36-hole totals of 132 on two occasions, the most recent in 2005. ... Park turned 25 on Friday. Fans in the grandstand at the 18th hole sang "Happy Birthday" to her as she walked off the green after sinking a short birdie putt. Park, who started her round on the 11th hole, smiled and waved to the crowd. ... Henderson and Jennifer Kirby of Paris, Ont., were added to the 144-player field as sponsor exemptions. Kirby and Charlottetown's Lorie Kane were at 5-under-par 137. Hamilton's Alena Sharp was the other Canadian to make it to the weekend, just making the cut at 3 under.