Lydia Ko produced a barnstorming finish to snatch a one-shot lead with a six under-par second round at the LPGA Marathon Classic on Friday.

The former world number one from New Zealand bagged back-to-back birdies on the 17th and 18th holes to leapfrog England's Jodi Ewart Shadoff for sole possession of the lead at Highland Meadows in Sylvania, Ohio.

Ko believes that being able to pick up strokes on the 17th and 18th holes at Highland Meadows -- both par-fives -- could be crucial over the weekend.

"To finish off with a couple birdies on the last two holes is nice," Ko said. "I think that's going to be the key for this golf course, and especially in the final groups, whether that's me or for any other players. Because it is two par-5 finishing holes, there could be a huge turnaround."

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Ko's pair of closing birdies bookended a blistering start to her round, when she reeled off four consecutive birdies over the first four holes to move into the lead.

Her roller-coaster 65 included nine birdies, three bogeys and six pars, leaving her at 13 under after 36 holes.

For most of the second round, it looked as if Ko would have to settle for a share of the lead with playing partner Ewart Shadoff.

The 32-year-old from Yorkshire was flawless in compiling an eight-under-par 63, making five birdies before the turn with two more on the 11th and 13th holes.

Ewart Shadoff then briefly took the lead with a birdie on the par-five 17th to move to 12 under, before Ko's strong finish left the Englishwoman a shot off the pace.

Ewart Shadoff said her game had benefited from playing with the in-form Ko.

"We get on really well, and obviously our games are kind of bouncing off each other," she said. 

"To play with each other tomorrow we'll have a similar vibe as today, so that's a nice feeling to have."

Ewart Shadoff's round follows her strong showing at last week's Drive On Championship at Inverness Club in Ohio, where she led going into the final round before fading from contention. 

World number two Danielle Kang, who had shared the overnight lead with Ko after an opening 64 on Thursday, had also looked poised to challenge at the top of the leaderboard with another blemish-free round.

Kang lost ground with a bogey on the 17th, however, before a birdie on the 18th gave her a four-under-par 67, to leave her in third on 11 under, two off the lead.

Ko, Ewart Shadoff and Kang have put clear daylight between themselves and the rest of the field.

The chasing pack is led by Mexico's Maria Fassi, who is fourth on nine under after a five-under-par 66.

Kristen Gillman and Megan Khang are tied in fifth place on eight under, five off the lead, while Australia's Minjee Lee is seventh on six under after a four-under-par 67 on Friday.