Spieth finished 13 under par at the windy Australian Golf Club to become the first American player to win the championship since Brad Faxon in 1993.
The 21-year-old birdied four holes on the front nine – three of them in a row – to lead by three strokes after nine holes, then made light of the challenging conditions by adding four more on the back nine, never threatening to lose his lead.
“It’s the best round I have ever played, especially considering the conditions,” Spieth said. “The golf course was in great shape, and it’s an experience I will never forget.”
Defending champion Rory McIlroy, who shot 76 on Saturday, finished with a two-over-par 72, 15 strokes behind Spieth.
McIlroy made two par-saving putts on both par-threes, the second and fourth, but had an eight-footer for birdie lip out on the third.
On the par-five fifth, he hit a perfect tee shot, but eventually went on to make bogey, effectively ending the defence of the title he won at Royal Sydney with a birdie on the last hole.
“It’s been tough all weekend,” McIlroy said. “I was trying to get something going but with the pin positions and the wind, it was just very hard to get the ball close to the hole. It just wasn’t meant to be this year.”
McIlroy was non-committal about returning in 2015.
???It depends all on the schedule and where it’s going, but I love playing in Australia,” McIlroy said. “I had a wonderful time this year, so hopefully it works again.”