New Zealand’s Lydia Ko unleashed a seven-under-par 64 to surge into a share of second place at the midway stage of the LPGA tournament in Malaysia.

The world No.3 compiled a bogey-free second round to climb from 16th overnight to within two shots of seventh-ranked Korean So Yeon Ryu, whose 65 lifted her to 11-under at the $US2 million ($NZ2.5 million) Sime Darby tournament.

Seventeen-year-old Ko, who matched her best round score as a professional, is level with Japan’s Ayako Uehara, England’s Jodi Ewart Shadoff and Korean Eun-Hee Ji.

Overnight leader Stacy Lewis, the US world No.1, could only manage even par on day two at the Kuala Lumpur Golf and Country Club to drop to a share of 11th.

Karrie Webb is the best-placed Australian at three-under-par.