BANGKOK, THAILAND - DECEMBER 07: Charl Schwartzel of South Africa plays a shot during round two of the Thailand Golf Championship at Amata Spring Country Club on December 7, 2012 in Bangkok, Thailand. (Photo by Athit Perawongmetha/Getty Images)

South African Charl Schwartzel seized control of the Thailand Golf Championship with a flawless second round 65 giving him an imposing four-shot lead over the chasing pack.

The 2011 Masters champion, who has battled injury for much of a disappointing season, returned to the clubhouse at seven under for the day to declare “half the job is done” after a high-class display at the Amata Spring course.

Racing against fading light after 90 minutes were lost to a downpour earlier on, the rangy South African hit birdies at 14, 15 and 16 to catapult him above impressive early second round leader Daniel Chopra.

“The other guys still got to catch me,” a beaming Schwartzel said before firing an ominous warning to his rivals ahead of Saturday's crunch third round.

“The way I'm feeling, the way I'm playing... there's no reason to slow down. It's been two good days. We'll see where it finishes.”

Schwartzel came second at last year's event to current world number six Lee Westwood, who posted a solid -- if unremarkable -- 69 to go in well off the pace at five under overall.

Twenty-five players will complete their second rounds early Saturday, among them home crowd favourite Thitiphun Chuayprakong who will resume stalking the leaders at nine under overall with three holes to play.

Earlier Sweden's Chopra surged to the top of the leaderboard, as big names including Westwood and Hunter Mahan failed to make an impact.

Chopra, who has not won on the Asian Tour for over a decade, sparkled for a second day at the Amata Spring course making six birdies in a five under 67, ending with an impressive 10 under overall.

“I guess coming back to Asia always brings out the best in my putter,” said the Swede, who grew up in India.

As the shadows spilled across the fairways, Japanese star Ryo Ishikawa -- bidding to secure his first overseas win -- showed why he is so highly-rated despite a disappointing season.

A slew of birdies on the back nine were only partly spoiled by a bogey on the last as the exciting 21-year-old returned a six under 66 to move into fifth place, one behind compatriot Masanori Kobayashi who is poised for a strong finish to his rookie Asian Tour year.

Ryder Cup hero Sergio Garcia was among a clutch of players on six under for the tournament, including Masters champion Bubba Watson whose two under 70 for the day threatened to be much better were it not for some loose putting.

“I let a couple of them slide with the putter,” the plain-speaking American said, adding he'll need two rounds of at least 65 over the weekend to get near the title.

But it was a disappointing day for star names Westwood and Hunter Mahan, who both started promisingly but fell away with late bogeys -- the US PGA star triple bogeying the last in a spectacular collapse.

Defending champion Westwood, who set last year's tournament alight with some of his best ever golf, finished in a three under 69, leaving him five shots off the lead after two rounds and needing a big day three to keep him in contention.

“I wasn't making anything. I've made nothing the first two days and left too many out there,” Westwood said bemoaning poor putting for his failure to recreate last year's sizzling form.

Mahan, a two-time US PGA tour winner this year, will be most disappointed after scorching seven early birdies only to collapse after the rain break, dropping three on a miserable final hole to leave him on four under overall. – AFP