Hansen shot 7-under-par 65 Saturday to make his total 13-under 203 before the rains came.
James Kingston (64) was second in the clubhouse at 12-under 204, with England's Steve Webster (66), the defending champion, at 11-under 205.
"We've almost been waiting for it all afternoon," Karlsson said when the horn sounded, stopping play until Sunday morning.
Karlsson, a back-to-back winner at the Mercedes-Benz Championship and Alfred Dunhill Links Championship, is closing in on Tiger Woods's record of three consecutive wins on the European Tour's international schedule.
The suspended round resumes Sunday at 7:50 a.m. local time (2:50 a.m. Eastern in the United States).