South Korea’s So Yeon Ryu fired a five-under-par 67 on Saturday to set a 54-hole tournament record and grab a four-shot lead after three rounds of the LPGA Canadian Open.

Ninth-ranked Ryu, the 2011 US Women’s Open champion, stood on 20-under 196 entering the final round at Ontario’s London Hunt and Country Club.

Ryu is bidding for a start-to-finish victory, having led by five shots after 36 holes following a course record 63 in the opening round.

With 21 birdies against a lone bogey over the first three rounds, Ryu is already below the tournament record score of 18-under-par by Norway’s Suzann Pettersen in 2009.

“I shot two-under and I feel like I lost 10 shots on the field,” Pettersen said.

Ryu, whose only other LPGA title came at the 2012 Toledo Classic, saw her course record matched by Spaniard Azahara Munoz, who shared second on 16 under with South Korean Choi Na-Yeon, who shot 66.

World No.2 Inbee Park, the South Korean star who captured her fifth career major title at last week’s LPGA Championship, was fourth on 14 under with Sweden’s Anna Nordqvist another stroke adrift.

Karrie Webb is the best-placed Australian at eight under in a tie for 13th.