Oosthuizen finished as a joint runner-up in the 2015 Open Championship at St Andrews after losing in a four-hole aggregate playoff during a Monday finish to the event. He was in the final group tied for the 54-hole co-lead but needed to birdie the 18th hole during his final round to tie the lead at 15-under and join Zach Johnson and Marc Leishman in the playoff. In the four-hole playoff, he birdied the first hole alongside Johnson, but could not convert his birdie putt on the second hole, giving Johnson a one-stroke advantage. All three players bogeyed the third hole and after Johnson missed his birdie putt on the final hole, Oosthuizen had a 15 footer to extend the playoff to sudden death. However his putt caught the lip on the low side and he finished at even-par, one stroke behind Johnson. This was Oosthuizen's second consecutive runner-up placing in a major championship, following the 2015 U.S. Open.