AUSTIN, Texas (AP) Everyone around him was telling Jason Day to withdraw from the Dell Match Play and not risk further injury to his back.
Day knew he was playing well enough to win and wanted to stick it out.
The decision paid off in more ways than he could imagine.
Day returned to No. 1 in the world by making it to Sunday. It felt even sweeter when he beat Rory McIlroy in an epic semifinal, and then beat Louis Oosthuizen in a championship match so one-sided that it might as well have been a victory lap around Austin Country Club.
''I'm glad I didn't listen,'' Day said. ''I wanted to win. I wanted to win so bad that I felt with how I was playing, if I kept playing the way I was going, I would be holding the trophy at the end of the week. And that's what kept me going.''
He's taking that confidence to Augusta National next week to start preparations for the Masters, which starts April 7. Coming off a victory last week in the Arnold Palmer Invitational, the 28-year-old Australian has won six times in his last 13 starts dating to the PGA Championship.
''It's been a memorable week, not only to win the Dell Match Play but to get back to No. 1 in the world,'' Day said.
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 for the championship match since it changed to 18 holes in 2011. Tiger Woods beat Stewart Cink, 8 and 7, in 2008 at Dove Mountain in a 36-hole match.
Oosthuizen, who knocked out Jordan Spieth in the fourth round to pave the way for Day's return to No. 1, won the opening hole with a par in the championship match and that was it. His only birdie was an 8-foot putt on No. 5 after Day had stuffed his wedge from the rough into 2 feet.
''A top player these days, he always makes that crucial putt when he needs to,'' Oosthuizen said. ''We've seen a thousand times through Tiger doing it. Jordan does it all the time. And Jason, whenever he needs to make a crucial putt, he makes it. You see him this morning against Rory when he made that putt on 18.
''He's always been a great iron player,'' he said. ''He's always been a great long iron player, and the way he's putting now there's a reason why he's No. 1 in the world.''
Day joined Woods and Geoff Ogilvy as the only multiple winners of the Match Play.
None of this looked possible when he winced and grabbed his back on the final hole he played in his 3-and-2 victory over Graeme McDowell on Wednesday. His caddie and coach, Colin Swatton, was standing near the tunnel leading to the first tee about 10 minutes before the match.
''I'm not sure we're going yet,'' Swatton said.
Day had therapy for an hour before and after each match. His back got progressively better, and so did his game. He played only 101 holes over seven matches - one match was six holes when Paul Casey withdrew Friday with a stomach ailment - and only had one match go the distance.
Rafa Cabrera Bello of Spain, who lost to Oosthuizen in the other semifinal, won the last three holes to beat McIlroy in the consolation match. The real consolation for the Spaniard was moving into the top 50 in the world ranking to earn a trip to the Masters for the first time.
Day might have won this tournament in the morning.
His semifinal match with McIlroy lived up to the hype. The lead changed seven times. They combined for 11 birdies in chilly, blustery conditions.
''I think the morning's round was probably one of the hardest rounds I've had to go through in match play format to try and get through,'' Day said.
The match turned on the 11th hole when Day got up-and-down for par with a 12-foot putt, while McIlroy missed a 6-foot birdie. Day got up-and-down eight times in his match against McIlroy. On the par-5 12th, McIlroy was first to hit and played well right of the green, away from the water. Day took on the hazard with a 2-iron that cleared the water by a foot and set up a two-putt birdie that gave him the lead for good.
He was 1 up going to the 18th, with thousands of fans rushing ahead to get a view. Day chipped away from the flag to ride the slope, hit it too hard and had a 12-foot putt for par. McIlroy was 6 feet away for par, hopeful of extra hole, until Day poured it in right in the middle.
''I knew if I could give myself a putt, I'd hole it,'' Day said.
He got up-and-down all eight times against McIlroy, and four out of five times in the afternoon against Oosthuizen. Because that's what No. 1 players do.