American Zach Johnson claimed his second major title with victory in a three-man playoff at the 144th Open Championship.
The 2007 Masters winner negotiated the four-hole playoff at the Old Course over holes one, two, 17 and 18 in one under to beat Oosthuizen by a stroke and Leishman by three.
Oosthuizen had a chance to extend the playoff, but he pushed his 10-foot putt just wide of the hole.
The trio finished 15-under at the end of their 72 holes, with Jordan Spieth a shot behind.
Kiwi golfer Ryan Fox finished with a flourish at the British Open, firing a final round five-under 67 to finish in a share of 49th at St Andrews.
Fox teed off stone cold last after a disastrous third-round 76 plunged him into a share of 78th place.
He opened with back-to-back birdies in benign conditions after torrential rain and winds battered the Old Course and resulted in a Monday finish for just the second time in championship history.
Fox added another birdie on the par-four ninth, then went on to collect two more before bogeying the 16th and finishing with a birdie on the last.
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