Golf: Lydia Ko in the lead at the LPGA Tour's Marathon Classic after first round

Lydia Ko hits her approach shot to the ninth green during the first round of the Marathon Classic. Photo / AP

A newly "aggressive" Lydia Ko has surged to take the lead after the opening round of the latest LPGA golf event in Ohio.

The Kiwi former World No 1 carded a seven-under par 64 at the Marathon Classic, to sit in a share of the lead with American Danielle Kang.

Ko, who shot eight birdies and a bogey, says her approach play was what helped her rocket out to a strong start.

"I hit a few shots that were really tap-in range," Ko said after her round. "So when you have three or four of those opportunities it definitely puts a little stress off the putter which was kind of the bit I was struggling with last week."

The 23-year-old said she worked with new swing coach Sean Foley on being more aggressive, which seemed to pay off on the course.

"Even if I am playing safe, I'm still being aggressive and committed over that shot," she said. "I think that's really important for me to be really committed and I'm hitting each shot with my 100 per cent authority and I know I hit it better that way.

"It's good to be back in this competitive atmosphere to kind of put that into play to see what you need to get better at.

"The confidence and being aggressive is something that I'm continuing to work on and is something that really helps me a lot out there."

Ko also said playing in front of no crowds, in what was the second LPGA Tour event since the Tour was suspended due to Covid-19, took some getting used to.

"Obviously we love seeing the fans," she said. "We're gutted that they're not here this year but hopefully next year they'll be back. But right now safety is priority and staying healthy."

Meanwhile, Danny Lee carded a one-under par 69 to sit four back of the lead, in a share of 33rd, at the PGA Championship major in San Francisco.

One of the leaders, Brendon Todd, is back at the PGA Championship after five years away.

Todd, who recovered from a wicked case of the yips that dropped him out of the top 2000 players in the world, won twice on the PGA Tour in the fall and now is among the top 50.

He made a 10-foot par putt on his final hole to join Jason Day at five-under. They were one shot ahead of nine players, including two-time defending champion Brooks Koepka, Justin Rose, Zach Johnson, Xander Schauffele and Martin Kaymer.

Nearly half of the field was at par or better, including Tiger Woods at two-under.

On the European Tour, Ryan Fox is in a tie for 34th, four shots off the lead at the English Championship after carding a four-under 67, while Michael Campbell shot a one-under 70 to sit in tied 92nd. Steven Alker sits in a share of eighth on the second-tier Korn Ferry Tour in the United States, after a three-under opening round.