Yani Tseng is back in a familiar position - at the top of the leaderboard.

Mired in a slump for the last few months, the world No. 1 shot a 6-under 66 on Thursday and is the first-round leader of the Canadian Women's Open at The Vancouver Golf Club.

Tseng won three of the first five events on the 2012 LPGA Tour schedule, but after a victory at the KIA Classic, she posted just three top 10s, and they came in the three events following that win.

Tseng missed three cuts in her last five starts prior to Thursday. She tied for 59th at the LPGA Championship and did marginally better at the U.S. Women's Open, where she shared 50th.

Last week at the Safeway Classic, Tseng came in 11th.

"I think that confidence is big," said Tseng. "It's very important for me. I mean, this week if I missed a couple of shots I don't worry about it, not like before. I feel like this is the way I used to play, so if I hit the best shot, I just try to recover from there. If not, if I make bogey, I try to make birdie the next hole, so I'm not worried.

"But like the last couple of months, it seems like I'm worried too much."

The reigning U.S. Women's Open champion Na Yeon Choi is alone in second at 5- under 67.

Amateur Lydia Ko and Inbee Park, who won the Evian Masters, are tied for third at 4-under 68.

They are all chasing the game's best, at least according to the rankings.

Tseng started on the 10th tee Thursday and rattled off back-to-back birdies at 11 and 12. She added another birdie at 18 to make the turn in good shape at 3- under par.

Trouble hit immediately.

Tseng double bogeyed the first hole when she tried to go over a tree with her second. She fell back to 1-under, but battled back to erase the disaster on her scorecard.

Tseng knocked her approach to a foot to set up an easy birdie at the fourth. She rolled in a long birdie putt at five, then converted a 4-footer for a third straight birdie at the sixth.

After a 4-foot par save at the par-3 seventh, Tseng closed with a 10-foot birdie putt at eight and a tap-in birdie at her last, which gave her the outright lead.

"I'm very happy with my round today, and very much looking forward to tomorrow and keep making birdies," said Tseng. "I wish I didn't finish today. I wish I could keep going, keep playing."

Angela Stanford, Mindy Kim, Moira Dunn and Jee Young Lee are knotted in fifth at 3-under 69.

Jiyai Shin, Sydnee Michaels, Christine Song, Vicky Hurst, Amy Yang, Paige Mackenzie and 2009 U.S. Women's Open champion Eun-Hee Ji share ninth at minus-2.

NOTES: There was light rain on Thursday, but there were no stoppages ... Defending champion Brittany Lincicome shot an even-par 72 ... Lorie Kane is the low Canadian at even-par 72 .. .Kris Tamulis withdrew on Thursday.