McIlroy delivered all the right shots in the playoff, smashing driver down the fairway and hitting 4-iron into 25 feet on the par-5 closing hole at Sheshan International to set up a two-putt birdie. Schauffele, who birdied the 18th in regulation to force a playoff, had to lay up from the rough near a bunker, and his 12-foot birdie putt stayed just right of the hole.
McIlroy won for the fourth time this year. It was his third World Golf Championships title, and his first since the Match Play at Harding Park in 2015. McIlroy played bogey-free over the last 39 holes and closed with a 4-under 68, taking trouble out of play down the stretch because he had the lead.
"Bogey-free on the weekend. I thought it would be enough to get the job done," McIlroy said.
Schauffele turned in a bold performance in his bid to become the first back-to-back winner of the HSBC Champions. He spent all week battling remnants of the flu, started the final round two shots behind and never let McIlroy feel in control.
Two shots behind with four to play, Schauffele birdied two of the last four holes for a 66, two-putting from the front of the green to a pin toward the back on the 18th in regulation, calmly making the 5-footer to force overtime at Sheshan for the second straight year.
They finished at 19-under 269.
Phil Mickelson closed with a 68 and tied for 28th. With Shugo Imahira finishing second on the Japan Golf Tour, Mickelson will drop out of the top 50 in the world for the first time since Nov. 28, 1993, the longest consecutive streak in the top 50 since the Official World Golf Ranking began in 1986. "It was a good run," Mickelson said. "But I'll be back."