Karlsson capitalized on a penalty stroke given to Ian Poulter.
DUBAI, United Arab Emirates (AP) -- Ian Poulter let the ball slip out of his hand, and with it went the Dubai World Championship.
Sizing up a 30-foot putt in the playoff, Poulter dropped his ball on his marker, moving it and incurring a one-stroke penalty that effectively gave the victory to Sweden's Robert Karlsson.
The bizarre turn of events Sunday at the $7.5 million, season-ending tournament was the climax of a day which saw as many as four players challenging England's Poulter for the lead. The 41-year-old Karlsson caught Poulter with a dramatic birdie on the 18th hole after he chipped within a few feet of the pin.
Karlsson calmly rolled in his short putt on the second playoff hole for the victory, his 11th on tour. He earned $1.25 million with the win while Poulter came away with $833,000.
Poulter, a colorful personality on the European Tour best known for his flashy attire, seemed as surprised as anyone by the gaffe. He described afterward how the ball slipped from his hand and fell two or three inches onto the marker -- a lucky coin featuring his children's names -- causing it to flip over and move from its original position.
"The coin was one way and the next minute facing the other way," Poulter said. "It's pitched right on the front and flipped over. If it pitches in the middle, the coin doesn't move and it's fine. But it's pitched on the front and it's flipped over."
Poulter spotted his error and reported it to the match referee, whose ruling left him with a long putt for par instead of a birdie. The putt came up a foot short, taking all the pressure off Karlsson as he then had two shots to clinch the victory.
"Ian Poulter called me over just after he had marked the ball on the 18th and told me he had dropped his ball onto the ball marker, which caused the ball marker to move, it just flipped over," chief match referee Andy McFee said.
Rule 20-1/15 is the one that trapped Poulter.
"Any accidental movement of the ball marker which occurs before or after the specific act of marking, including as a result of dropping the ball, regardless of the height from which it was dropped ... results in the player incurring a one stroke penalty," McFee said in a statement.
Karlsson, who was made aware of the penalty before Poulter putted, admitted he would have rather not won by default.
"These things happen in golf. It's not the way you want to win," he said. "The rules are there for a reason, but some of them can be tough."
Poulter's mistake was the main talking point among players afterward, with some sympathizing with him and others finding humor in his misfortune even if it did cost him more than $400,000.
Poulter's friend and rival Rory McIlroy tweeted: "Poults may not have won the Dubai world championship, but he could be in with a shout for tiddlywinks world championship."
The victory for Karlsson was his biggest and most lucrative yet.
"This must be the highest one I would think if you just look on the quality of the field that's been here, world No. 1, world No. 3 or 4 or whatever it is," he said.
The winning putt was Karlsson's third straight birdie on the 18th green, having caught up to Poulter on his last hole in regulation when his approach shot landed within a few feet of the pin. He rolled that in to close with a 5-under 67 and a 14-under total of 274.
Poulter then had a birdie putt for the victory at the 18th but missed it just wide to force the playoff, where both players birdied the first hole.
"I felt I hit a very good putt," he said of the near-miss at the 18th. "Six inches short of the hole, I would have probably put my house on it, but it slows down and takes a little bit of grain and misses. Obviously a little disappointed, and it was a shame it's just ended the way it has. Robert has hit a good third shot, and you know what, he stepped up and holed the putts. So every credit."
Karlsson led after the first round but followed it up with a 75 on Friday to seemingly fall out of contention. He recovered with consecutive rounds of 67, and started Sunday with consecutive birdies. His second shot on the par-4 third then landed on the green and rolled in for an eagle.
He had two more birdies on the back nine before a lovely approach shot almost hit the pin on the 18th, spun back and landed within a few feet of the hole.
The No. 1-ranked Lee Westwood came up a shot short and finished in a tie for third with Spain's Alvaro Quiros after his approach shot to the 18th green landed in the water and he had to scramble to save par. Quiros missed an eagle putt on the 18th that would have pulled him into the lead while McIlroy shot an eagle on the 18th to pull within two shots of the lead. He finished in fifth.
Despite his disappointing finish, the 34-year-old Poulter said the tournament provided a fitting end to the season with some of the best in Europe all in the mix almost until the end.
"It was good. Looking at the board all the way around, Robert got off to an incredible start, birdie, birdie, eagle. Westy made a late charge. It was good fun the whole way around," Poulter said. "I felt good, hit lots of good golf shots. I made a couple of key up and downs at the right time. But, you know what, you're left walking away disappointed."