Jason Day made his return to No. 1 in the world feel even sweeter Sunday by winning the Dell Match Play.

Day outlasted Rory McIlroy in an epic battle in the morning semifinals by making a 12-foot par putt on the 18th hole. The championship match against Louis Oosthuizen turned into a victory lap at Austin Country Club.

And to think Day thought about pulling out Thursday morning when his back seized up on him. Three days later, he looked better than ever.

Day pulled ahead with a 10-foot birdie putt on the par-3 fourth hole, stretched his lead to 3 up at the turn and was relentless with his power and short game the rest of the way. He closed out Oosthuizen with a wedge to 3 feet for a conceded birdie on the 14th hole and a 5-and-4 victory.

It was the largest margin in the championship match since Tiger Woods beat Stewart Cink, 8 and 7, in 2008 at Dove Mountain in a 36-hole match.