Brandt Snedeker was on the tee at No. 7 when he noticed something wasn't quite right.

He couldn't find fellow American and second-round leader Hunter Mahan's name at the top the RBC Canadian Open leaderboard.

"I looked at my caddie, and I go, 'What's going on?"' Snedeker recalled. "He goes, 'I think Hunter had to leave because (his wife) went into labour."'

His caddie was right.

Mahan, the tournament leader after 36 holes, abruptly withdrew to rush home to Dallas for the birth of his first child on Saturday and Snedeker took advantage by shooting a sizzling 63 to vault himself into the lead after the third round at Glen Abbey Golf Club.

"(It) just kind of left the tournament wide open," Snedeker said of Mahan's withdrawal. "Hunter was going to be hard to catch because he was playing so good. The way he drives the golf ball on this golf course, he was going to play really well on the weekend. For me to catch him, I knew I was going to have to shoot something really low."

Mahan, who was in the final group at both the U.S. Open and British Open, had a two-stroke lead at 13 under after following up Thursday's 67 with a 64 on Friday. He was getting ready for his third round when he got word that his wife, who was not due for another four weeks, had unexpectedly gone into labour.

"It just changes the complexion of the tournament because Hunter had been playing so well, he was going to be a tough guy to catch. Now that he's not here it's kind of wide open," said the 32-year-old Snedeker. "Anybody can win this tournament."

Lingmerth, Kuchar lurk

Sweden's David Lingmerth fired a 65 on Saturday and is a stroke back of Snedeker, while Matt Kuchar (64) and Jason Bohn (66) both sit at 12 under at the par-72, 7,253-yard course.

Snedeker opened the day with an extraordinary front nine that saw him make the turn at 29 with six birdies. He continued his strong play on the back with three more birdies for a bogey-free round.

"You always feel like you're exactly one swing away from hitting something off the planet or something like that," Snedeker said. "I felt like I managed my game really well today."

Kuchar, a father himself, said he couldn't recall a 36-hole leader withdrawing from a tournament for any reason.

"The birth of a child is a truly magical, special thing. You may get it once in your lifetime. It just doesn't happen that often," Kuchar said. "Hunter right now is playing some of the best golf in the world. It kind of gives the rest of us a chance with him not in the field."

Dustin Johnson also shot 63, good for a tie for fifth at 11 under with John Merrick (72), Greg Owen (67), Charley Hoffman (67) and Kyle Stanley (66) on a day that saw scattered showers and an 80-minute weather delay due to lightning.

Merrick, who finished the second round two strokes back of the lead after tying the course record with a 62, was forced to play alone in Saturday's final grouping after Mahan's departure. He bogeyed four of the first seven holes but rebounded with birdies on Nos. 15 and 16 and an eagle on No. 18 to finish the day at even par.

David Hearn makes cut

Players who began their rounds early in the day benefited from calm conditions, including David Hearn of Brantford, Ont., who shot 68 to move to 5 under.

Hearn made Friday's cut by birdieing his final three holes to finish the first two rounds at 1 under. He kept that strong play going on Saturday with a birdie on the first hole and six overall to sit tied for 39th.

"I felt good yesterday finishing the way I did," said the 34-year-old Hearn. "I didn't play my best getting to the weekend but it's a pretty tight leaderboard."

Mike Weir of Brights Grove, Ont., shot a disappointing 73 after Friday's 67 and is 3 under in a tie for 55th.

"It was kind of adventurous and not very profitable at all," the 43-year-old said. "Didn't make anything again and struggled a little bit at times. Just never seemed to get in the flow of the round."

Roger Sloan of Merritt, B.C., shot 72 and sits at 2 under after three rounds in a tie for 62nd.

The 26-year-old, who plays on the Web.com Tour but earned an exemption into the tournament, played with former champion Vijay Singh, who was 8 under through 13 holes before settling for a round of 66.

"(Singh) was just a gentleman. He was a real class act," Sloan said. "It was real nice to play with him. He keeps the game real simple: Fairways, greens and putts. Pretty simple game."

Snedeker, the 2012 FedEx Cup champion whose best-ever finish at a Canadian Open was a tie for fifth at Glen Abbey in 2009, predicts that scores will drop even further on Sunday.

"I'm going to have to shoot 4, 5, 6 under par to have a chance to win. That's just the way the golf course is playing," he said. "It's playing perfect. It's a lot of fun to play. If you're playing well, you're going to make a lot of birdies. If you're not, you're going to struggle.

"I think 18, 19, 20 under par is going to be the score to get to, and I'm going to try to get past that."