Tseng, the 19-year-old Taiwanese star who won the McDonalds LPGA Championship in early June and finished second two weeks ago in the Womens British Open, had a 14-under 202 total on the tree-lined Ottawa Hunt and Golf Club course.
Every week Im ready to win the tournament, Tseng said. I finished second four times and I really learned a lot each time. I dont feel surprised because I keep learning and working hard and being relaxed.
I have to play my own game and not think too much. I have a four-shot lead, so theres a lot of room to play good.
Se Ri Pak (68) was second, and defending champion Lorena Ochoa (74) and Katherine Hull (72) were 8 under. Paula Creamer (70) and Song-Hee Kim (71) were 5 under.
Pak had her first LPGA Tour hole-in-one, acing the 178-yard fifth with a 6-iron.
It was a surprise to see it go in, said Pak. Of course, you dont expect anything like that. That probably made my day.
Michelle Wie, using the last of her six LPGA Tour exemptions this year, was tied for 14th at 2 under after a 69. She opened with rounds of 75 and 70.
Im making a lot more putts than I did the first day, Wie said. All I can do is play the best I can and try to shoot a low score. Ill focus on being consistent, hitting fairways and greens.
Annika Sorenstam (76) and Suzann Pettersen (70) also were in the group at 2 under.
I feel fine. I just didnt play well today, Sorenstam said. I actually hit a lot of good shots, I just never converted. Obviously, Im very disappointed.
Tseng returned to the course early Saturday to finish the final eight holes of the second round. She birdied the final four holes to break the course record of 65 set by Martha Nause in the 1994 du Maurier Classic and matched Friday by Hull.
Tseng had seven birdies and three bogeys in the third round.
I feel great, but Im so tired, Tseng said. It was such a long day and I had a headache, so I just tried to concentrate on every shot.
Ochoa birdied the final hole.
It wasnt a great day, the top-ranked Mexican star said. I didnt hit the ball good and I didnt putt good. I made birdie on the last hole and have a little chance now. Theres nothing I can do. Just come here tomorrow and do my best.
Alena Sharp was the top Canadian. She was 1 over after a 73.
You always want to shoot under par, said Sharp, from Hamilton, Ontario. Im out of contention to win now, but I still feel I can shoot in the 60s out here and that would be a great way to finish'to get back into red numbers.
Compatriot Lorie Kane was 4 over after a 73.