Twelve shots better than his back nine, Singh finished with a 68 and was two shots behind Joey Sindelar, who finished his 66 late Thursday.
Singh, among half the field who failed to finish the first round because of a five-hour rain delay, hit his approach into the water and took bogey on the 18th to shoot 40 on his opening nine. He was in jeopardy of missing the cut in his first event since replacing Tiger Woods at No. 1 in the world ranking.
All that changed on the front nine, played under gorgeous sunshine and little wind.
Starting with a 3-foot birdie on the second hole, Singh played the next seven holes in 7 under par. He made five birdies inside 6 feet, and holed a 40-foot eagle putt on the fifth.
His 28 broke by one shot the Canadian Open record for nine holes, previously held by Mike McCullough in 1984 and Andy Bean in 1983, both times at the Abbey.
Singh had a 25-foot birdie putt on his final hole that would have tied the PGA Tour record of 27.
It was an even better performance by the last No. 1 player at Glen Abbey. Four years ago, Woods was close to the cut line in the second round when he finished birdie-eagle-birdie-eagle to shoot 65, and he went on to win.
Just as suddenly, Singh again looks like the man to beat.
He declined comment after his record-setting nine holes - 'Not now,' he said to a Royal Canadian Golf Association media official - and headed back out to start his second round.
Billy Andrade, who won a dramatic playoff in 1998 at the Abbey, also turned around his fortunes by playing his final 10 holes in 6 under par for a 67, leaving him one shot behind along with Craig Barlow.
The biggest star, former Masters champion Mike Weir of Canada, recovered from a double bogey on the eighth hole to shoot a 68, his lowest round at Glen Abbey and the second time he has shot in the 60s on the Jack Nicklaus design that has never been one of his favorites.
Singh and the other players who had late starts Thursday and didn't finish the round caught a huge break. They returned Friday morning to pristine conditions that replaced 30 mph gusts, allowing for only a dozen scores under par.
Sindelar, who won earlier this year at Wachovia to end a 14-year drought, did not tee off until 4:25 p.m.
He had every reason to lose his patience Thursday.
The Canadian Open is his sixth consecutive tournament, and he hasn't played any of them particularly well. Then, he had to wait through five hours of rain delays before he could tee it up, turning a morning round into an afternoon round with vicious gusts.
Ultimately, it turned out to be a lovely day.
Sindelar made the Abbey look like a breeze with his 5-under 66, giving him a two-shot lead over Pat Perez among half the field that finished the first round.
'Through this five weeks, I haven't done well,' Sindelar said. 'But my swing feels very, very good. I'm hitting a lot of shots right at it, which tells me my swing plane is OK. I drove the ball well, stayed out of trouble, hit a lot of greens. Everything went as I hoped it would.'
David Duval took another step emerging from his slump - not because he shot an even-par 71, but because he was upset about it.
'That's a good place to be - not happy about an even par on a day like this,' Duval said. 'That's a lot of progress from where I was a couple of months ago.'
On the other side was Perez, who managed to keep his cool despite being known for his hot temper. Perez had food poisoning Wednesday and almost withdrew, so the rain delay helped him - and so did five birdies after starting the tournament with a three-putt bogey.
'Old me would have gone to the car,' Perez said. 'I didn't get mad today. I've been working on not getting as mad and frustrated, just waiting for it all to come together.'
Sindelar made three straight birdies around the turn - one of those a two-putt from 4 feet after reaching the par-5 18th with a 6-iron. He missed the green long on No. 2 for a bogey and was headed for another one on the par-5 fifth until he rolled in a 50-footer from the fringe for birdie.
Masters champion Phil Mickelson started and finished his round with a birdie, but made a mess of it in between in his debut with a new golf ball, driver and fairway metals after signing with Callaway this week. He took a double bogey on No. 8, made five other bogeys and shot 75, matching his highest score of the year.
'I knew I was rusty,' said Mickelson, coming off a two-week break.
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