Rory McIlroy fought back from three down to beat Lee Westwood 3&1 in their semi-final clash at the Accenture Match Play Championship in Tucson.
And it means the the US Open champion can now go to world number one if he beats Hunter Mahan in the final later today.
Westwood made the early running, winning the second with a five foot birdie putt and the third after McIlroy couldn't save par from sand.
Another birdie putt at the fourth put Westwood three up but a bogey at five gave McIlroy his first gain and from that point on the Northern Irishman never looked back.
He won the next with a birdie putt from 28 feet, made the match all square with a 15 footer for birdie on the eighth and made it a third birdie in four holes at the ninth to turn turn one up.
After 10 and 11 were halved, McIlroy pressed the accelerator again and produced winning birdies at 12 and 13 to go three up.
Westwood won his first hole since the fourth with a birdie at 15 to cut the gap to two down but, after the 16th was halved, he handed McIlroy the match via a bogey at the long par four 17th.
Always in front
In the other semi-final, Mahan was always in front after winning the first via a bogey from fellow American Mark Wilson.
Mahan won the next to go two up but could never build a significant lead.
Wilson, a winner of the Humana Challenge earlier this year, three times reduced the lead to a single hole, once with a birdie at five and twice with par threes at three and 12.
But when Mahan won the 15th with a birdie three to go two up again, Wilson couldn't rally for a final time. Pars at the 16th and 17th were enough to give Mahan a 2&1 win and secure his place in the final.