Kuala Lumpur - Pat Perez posted a seven-under-par 65 to take the second-round lead of the rain-interrupted CIMB Classic on Friday as defending champion Justin Thomas slipped further behind.
American Perez fired home eight birdies to take him to 13-under-par 131 after day two at the TPC Kuala Lumpur, where play was stopped for almost four hours due to a tropical thunderstorm.
Compatriot Xander Schauffele was one shot behind, after starting strongly with an eagle on the third hole to pave the way for five-under-par 67.
It was another disappointing day for Thomas, who is hoping to win a third consecutive title at the event.
The American is coming off the back of a breakthrough season which saw him rack up five wins, including a maiden major victory at the PGA Championship in August.
After posting 70 in the first round, he scored a one-under-par 71 on Friday, leaving him tied for 33rd place, and 10 strokes off Perez.
Friday's score - which included two bogeys and a double bogey on the 12th hole - equals his worst round in his CIMB Classic career.
But it was a great day for Perez, ranked 31 in the world, who said his good putting propelled him to the top of the leaderboard.
"Anytime you're trying to win you've got to putt well. So the guy that wins hits it pretty good, but he putts the best, he scores the best," he said.
"I've got to try to do the same thing on the weekend."
PGA Rookie of the Year Schauffele said he stumbled after the lengthy interruption of play, but could still mount a serious challenge.
"Made some mistakes, I think everyone did," he said.
"Everything is kind of right where it needs to be - I'm not doing anything stupid. I'm just comfortable."
Overnight leader Cameron Smith, South Korea's Kang Sung-Hoon and Belgium's Thomas Pieters were in tied third place on 135.
Anirban Lahiri was another favourite who underperformed Friday.
The Indian, who won the Malaysian Open on the same course in 2015, faltered on the back nine with three bogeys to finish with a one-over-par 73.
The CIMB Classic is co-sponsored by the Asian Tour and PGA Tour.