SAN FRANCISCO (AFP) - World number one Rory McIlroy produced a scintillating late comeback to beat Billy Horschel and advance to the knockout stage of the WGC-Championship Match Play in California on Friday as rival Jordan Spieth crashed out.

Northern Irishman McIlroy seemed to be following Spieth out of the tournament at Harding Park after finding himself two down with two holes to play against Horschel in the Group 1 decider.

But a magnificent long birdie putt on the must-win 17th ignited a late charge from McIlroy who then won the 18th before prevailing on the second hole of sudden death.

McIlroy said he had drawn inspiration for his crucial birdie putt on the 17th from a similar situation at last year's Ryder Cup.

"I remembered I holed a putt I think on the 17th at the Ryder Cup last year when I was playing with Sergio (Garcia) and it was same sort of thing where I knew I had to hole it or I was going to get beaten," said McIlroy.

"So I drew a bit of inspiration from that and hit the best putt I made all day. When we got to 18, I knew I just had to keep the pressure on him and somehow I was able to turn it around."

McIlroy will now face Hideki Matsuyama in the last 16 on Saturday and believes the Japanese 16th seed will need to produce something special.

"I haven't made that many birdies but I think over the last few days, I've made only one bogey," he said.

"So if guys want to beat me, they're going to have make birdies."

Fans hoping to see McIlroy face off with Masters champion Spieth over the weekend were left disappointed after the 21-year-old US prodigy lost in a tight duel to England's Lee Westwood.

European Ryder Cup star Westwood recovered from losing the opening two holes to go one up after draining a 10-foot birdie putt on the 17th.

Spieth was unable to wrest back the initiative on the 18th, giving Westwood a two-up victory and allowing the 42-year-old English veteran to advance.