Karlsson opened the final round three strokes behind Poulter but rallied for a 5-under-par 67 Sunday to get to 14-under 274, tying Poulter who shot 2-under 70 Sunday. Both players had birdies the first time they played the par-5, 620-yard 18th hole in the playoff.
But the second time around, Karlsson knocked his third shot within 4 feet while Poulter was 30 feet out. Poulter was assessed a 1-stroke penalty for dropping his ball on his marker and moving it. He ended up with a 6 on the hole and Karlsson made his short putt to claim his 11th European Tour title.
Karlsson pulled into contention by opening Sunday with two birdies and an eagle on the par-4 third hole. He had bogeys at Nos. 4 and 6 but also started his second nine with back-to-back birdies and added a birdie at No. 18 to get to 5-under on the day.
Poulter had a bogey at No. 3 -- only his third of the week -- and birdies at Nos. 7, 11 and 12 en route to his 70.
Alvaro Quiros, who shot 67 Sunday, tied with Lee Westwood (68) for third place at 13-under while Rory McIlroy (67) took fifth another stroke back.
Martin Kaymer ended up tied for 13th at 6-under but that clinched the yearlong European Tour title for him. Kaymer, who turned 26 on Dec. 28, is the youngest European No. 1 in 31 years.