The South African looked like the favourite before the start of the fourth round when he went out in the final pairing with Irish amateur Paul Dunne and battled doggedly to set-up a three-way playoff with Zach Johnson and Marc Leishman.
Needing a birdie on the 18th to match Johnson's one-under total for the four-hole playoff, his 10-foot putt refused to break right, bringing to an end a memorable final day.
It was Oosthuizen's second near miss in quick succession after sharing second place at the U.S. Open last month.
"The front nine, you could see everyone was scoring on the front nine, and I was only -- I went through in two-under, and that back nine was tough," Oosthuizen said.
"When we made the turn on 12, St Andrews showed its teeth."
Oosthuizen, whose final 54 holes at Chambers Bay last month was the lowest in U.S. Open history but still left him short, seemed to be closing in on the Claret Jug when he rolled in a birdie at the 12th to reach 15 under.
After that, he was hanging on as a course that was so generous on Sunday, hit back.
A superb par at the brutal 17th and a sweet approach to the 18th, which he then calmly birdied, seemed to put him in the driving seat as he joined Johnson and Leishman back on the first.
But he was to suffer his second playoff heartache after also losing one at Augusta in 2012 to Bubba Watson.
"It's never nice to lose a playoff. I've had the experience in 2012 at Augusta," he said.
"But yeah, I'll take a lot out of this week. I was really motivated to win this championship. I love this place. I've said it a thousand times.
"I can't wait for it to come back here again."
Despite coming joint-second, Oosthuizen said it had been a great major to be part of.
"Probably one of the most exciting Opens," he said.
"A lot of guys will take a lot of good out of this. It'll be great for golf if this is going to be the way forward."
(Reporting by Martyn Herman, editing by Gene Cherry)
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