World number two Ko Jin-young surged to the top of the leaderboard on Friday with a five-under 67 to take a one-shot lead at the halfway stage of the LPGA Portland Classic.

Ko, who is playing in her first tournament since failing to win a medal at the Tokyo Olympics, rolled in six birdies, including back-to-back efforts at the 13th and 14th, with the only blemish a bogey on the par-four 11th.