Ochoa, the winner last year at Royal Mayfair in Edmonton, Alberta, hit all 18 greens in regulation and was in the rough only once in sunny, calm conditions on the tree-lined Ottawa Hunt and Golf Club course.
Youve got to be careful off the tee ' to hit the fairways ' thats going to be the key all week, said Ochoa, a six-time winner this year.
The 18-year-old Stanford student, down to No. 309 in the world, needs to win or finish second to avoid a trip to Q-school ' if she decides to try qualifying.
In her last start, she missed the cut in the PGA TOUR's Reno event with rounds of 73 and 80. In the State Farm Classic in her previous LPGA start, she was disqualified for failing to sign her second-round scorecard.
Se Ri Pak, Nicole Castrale, Meena Lee and Hee-Won Han opened with 68s, and Suzann Pettersen, Catriona Matthew, Song-Hee Kim, In-Kyung Kim and Eunjung Yi had 69s. Lee won the 2005 tournament at Glen Arbour in Halifax, Nova Scotia.
Canadian star Lorie Kane had a 74.
Sorenstam, the 2001 winner at Angus Glen in Markham, Ontario, had six birdies and a bogey for a 5-under 31 on her first nine, the back nine. The Swede dropped strokes at the second and eighth before closing with a 14-foot birdie putt on the par-5 ninth.
I putted really well, said Sorenstam, leaving the tour after the season. I got off to a great start and made tons of putts. I missed a few opportunities on the (second) nine, but I made a birdie to finish on a high note, so Im very pleased.
She had only 10 putts on her first nine holes.
I cant remember the last time I had 10 putts on nine holes, Sorenstam said. Thats what you need to score here.