Justin Rose moved four shots clear going into the final round at the BMW Championship in Illinois.
The Englishman began the day level on 11 under par with Mark Wilson, but where Rose carded a two under 69 to edge further clear, Wilson suffered a nightmare six over 77 to plummet into a share of seventh place.
"I was aware today that it was a pretty tricky day and guys weren't going low," Rose said.
"I'm pretty happy to get it in where I was."
Rose is aware that he has thrown away such a lead before on the final day.
"I've been there a little bit last year - won one, lost one when I was in a situation like this," he said. "So I've got some good experience on which to count on. Just keep seeing good shots and keep playing one shot at a time. I don't think you can get defensive. A four-shot lead isn't really a big enough lead to waste holes."
Rose's round was largely uneventful as back-to-back birdies on the fourth and fifth quickly boosted his advantage and he quickly cancelled out a bogey on the 12th with a birdie on the 13th.
His scorecard was otherwise unblemished, with the solid effort leaving him comfortably ahead of second-placed John Senden, who signed for a 70, using four birdies on the back nine to recover from a shocking start that saw him bogey three of the opening five holes.
Geoff Ogilvy is up to third after an impressive three-under 68 saw him improve to eight-under for the tournament, level with Bill Haas, who suffered a double-bogey on the 16th to drop out of a share for second, having used an eagle on the 11th to climb up the standings.
Webb Simpson began the day in second place, but his disappointing round of 73 dropped him to fifth on seven under, one shot ahead of Keegan Bradley.
The best rounds of the day belonged to Sergio Garcia and Luke Donald, who each went round in 67, four under par, to climb all the way up to a share of seventh, having been 20th.
Garcia had an up and down day, but an eagle on the par five 15th helped him overcome three bogeys on his scorecard. Donald also had two bogeys, but six birdies helped him make up ground on the leaders.
Donald is recovering from an opening day 75 with rounds of 66 and 67 the last two times out.
"I drove it better, high irons better, I putted better, my short game was better," Donald said when asked what had changed.
"None of it really worked very well the first day for some reason. I just got off to a horrible start. I'm proud of myself to get back in it and at least give myself a sniff."
Rose added: "It's never easy after a 63 to come out and go low again and on this course I'd certainly take anything in the 60s almost any day you play it. So to come out and shoot 68, I'm very delighted with that.
"At a couple of key points in the round today when things were going a little flat for me I managed to make two birdies back to back and then went eagle-birdie on the back nine too. I'm very happy."
Rose needs a good finish to ensure he is one of the 30 players to qualify for next week's Tour Championship and added: "In golf you never know, you can just give yourself the best shot and the way to do that is to be mentally as good as you can and stay as patient as you can.
"It's easy to get frustrated on weeks like this when you have to make something happen, but to this point I managed to stay really calm and under control and it's paying off."
