LOS ANGELES-Thailand's Ariya Jutanugarn roared back to form with a superb eight-under-par 64 to claim a three-shot lead at the Canadian Pacific Women's Open on Friday.

British Open champion Ariya limped out of the Olympics last week after a knee injury derailed her bid for a medal after she had taken a first-round lead. But the talented 20-year-old rediscovered her best form in sunny conditions at Calgary's Priddis Greens Golf and Country Club to storm to the top of the leaderboard.

The Thai youngster, enjoying a breakthrough season with four victories and nine top 10 finishes, carded eight birdies and no bogeys in a flawless round which left her at 12 under for the tournament. Ariya said her sore knee had improved gradually over the course of the week following her withdrawal in the third round in Rio. "I feel like I'm okay. I wanted to see how I'm feeling. But after that, like on Monday, it didn't hurt that much and today it's getting a lot better," she said.

South Korea's Chella Choi Woon-Jung had started the day in sole possession of the lead, completing her weather-disrupted first round to finish with a seven-under-par 65. But Choi was unable to build on her lead in a rollercoaster second round, notching four birdies and three bogeys to finish with a one-under-par 71, four off the lead.

South Korea's Chun In-Gee was three behind Ariya on nine under after a see-saw five-under-par round which included an eagle, six birdies and three bogeys. Northern Ireland's Stephanie Meadow -- who lit up the first round with a 66 -- was also three back after a second round 69.

Five players finished the second round on eight under, four adrift of the lead. They included New Zealand's world number one and defending champion Lydia Ko, who is gunning for her fourth victory in the tournament.

Ko appeared to be building a head of steam with four birdies in a row between the ninth and 12th holes to move to nine under. But a bogey on the 14th checked her momentum as she finished the day four behind.