Playing in the same group, Karlsson and Ross Fisher stood at 14 under through 16 holes when play was stopped ahead of an approaching storm around 4:50 p.m. local time (11:50 a.m. ET). Alvaro Quiros was also 14 under on his 14th hole.
The three co-leaders were one shot ahead of Soren Hansen, who held the clubhouse lead at 13-under 203. Hansen finished off a seven-under 65 ahead of the storm.
Chasing his first Order of Merit title as the European Tour's leading money winner ' he currently leads the race ' Karlsson put the impending storm out of his mind long enough to make birdies at the 12th, 14th and 15th holes.
The birdies gave him a share of the lead not long before the horn sounded to stop play.
'We've almost been waiting for it all afternoon,' Karlsson said later. 'It looked like it was going to miss, and then maybe more like it was coming.'
Karlsson is coming off victories at the Mercedes-Benz Championship and Alfred Dunhill Links Championship and is closing in on Tiger Woods' record of three consecutive wins on the European Tour's international schedule.
The back-to-back titles have come at the tail end of a career season that has seen Karlsson post nine other top-10 finishes, including three in major championships.
Looking to become the first Swede to ever win the Order of Merit, Karlsson still has 20 holes remaining to play at Oceanico Victoria Golf Course. And there's at least one familiar foe standing in his way.
He and Fisher are becoming quick rivals, having faced each other as part of a three-way playoff at the Alfred Dunhill Links Championship two weeks ago. Karlsson made a birdie on the first extra hole to defeat Fisher and Martin Kaymer.
'I'm playing well but I must keep it going,' said Karlsson.
James Kingston fired an eight-under 64 and was two shots behind the co-leaders ' and one back of Hansen ' at 12-under 204. Steve Webster had a 66 and was another shot further back at 205.
Second-round leader Stuart Manley was among three players on the course at 11 under par when the round was suspended.