The giant Swede, who has yet to make a bogey in this year’s tournament, stands on 12-under-par 128 after another blemish-free round at the Hong Kong Golf Club in Fanling.
Former Hong Kong champion Miguel Angel Jiménez is on eight-under 132 while nine players – including 2003 Masters champion Mike Weir – are a shot further back.
“It’s definitely been pretty good,” said Karlsson. “It’s great to be in this position and I’ve played really well over the first two days.”
Karlsson has never previously had any success around Fanling’s tight par-70 Championship layout and was particularly frustrated by his last visit to the course in 2005.
He played both pro-am tournaments this week in an effort to put that right and decided to rein in his natural big-hitting game. The tactic is paying off so far.
“It’s a course where if you’re trying to overpower it you’re going to be in all sorts of trouble,” said the Ryder Cup star.
“My caddie said to me, ‘If I’m going to come with you to that course, we’re going to change something radically.’ And we have because he had a tough time the last time here – I had a bit of a bad temper then!
“But we put in a bit of extra time in the preparation. We played both the pro-ams to see if we could figure out how to get round it a little better.
“I’ve understood exactly what I need to do to have a good score around this golf course and then it’s up to me to do it. So far I’ve done well. I used my driver only once today, at the sixth.”
Jiménez, the Hong Kong champion three years ago, was happy after adding a 67 to his opening 65.
“I always say if you make under par it is good,” said the cigar-chomping, pony-tailed Spaniard.
“I played really well on the back nine, my first nine, to be out in 32. Overall I’m satisfied with the way I hit the ball and with the way I played, I just need a few more putts to drop over the weekend.”
Jiménez said he was happy to be back on a course where he has enjoyed previous success. He finished joint sixth last year in addition to his 2004 triumph.
“I always enjoy this golf course,” he said. “It’ a great old-fashioned course where you have to be safe from the tee to allow you to have a chance for the green. You have to concentrate hard here and I like it.”
The chasing pack at the UBS Hong Kong Open includes some big-name players.
Canada’s Weir showed the form that has brought him eight PGA Tour titles with a superb 64.
He was joined on seven-under 133 by his fellow PGA Tour star Trevor Immelman, who rocketed into contention with a brilliant 62 – the lowest round of the day.
“I needed something special,” admitted the South African. “I got off to a nice start with a birdie on the second hole.
“On the eighth hole, I started to hit great iron shots and the only one I think I missed was on the 17th hole where I was right on the line but I didn’t hit it hard enough.
“My scores have been awful the past couple of weeks, but I worked hard on the range yesterday and something started feeling good.
“A lot of times, when something is good on the range, you can’t take it to the course the next day. But today I felt comfortable and that was nice.”
Chinese No.1 Liang Wenchong had the galleries cheering with a 66 that left him on six-under 134.
Liang, the current Asian Tour UBS Order of Merit leader, is seeking to become the first mainland player to win the Hong Kong title.
First-round leader KJ Choi of Korea faltered on Friday, adding a 72 to his opening 62 to stand level with Liang.
But two-time US Open champion Retief Goosen made his move with a 66 that left him on five-under 135 and poised to make a charge at the weekend.
With a strong contingent from the PGA Tour, the field for the 2007 UBS Hong Kong Open – again jointly sanctioned by the European and Asian Tours – is the strongest in the tournament’s history.
The Open was first staged in 1959 – making it the territory’s oldest professional sporting event – and has been held every year at the Hong Kong Golf Club.