Jason Day remains on course for his first BMW Championship title and the world number one spot after opening up a six-shot lead heading into Sunday's final round in Chicago.
The Australian tied the all-time PGA Tour record with an 18-under 124 in the first two rounds and he picked up another two shots on Saturday with a third-round 69.
Another steady round for Day would likely seal a fourth win in six tournaments, which would see him replace Rory McIlroy at the top of the rankings.
The Northern Irishman began the round nine shots behind Day and only managed to claw two back with a four-under 67 to sit fourth, with American duo Scott Piercy and Daniel Berger one shot better off.
World number two Jordan Spieth carded a one-over 72 to lie 10 under overall as he saw his hopes of victory in Chicago - and his own chances of usurping McIlroy - slip away, with Englishman Justin Rose a shot further back after going round in 70.
Brendon Todd, playing alongside Day and Berger in the lead group, dropped dramatically from second to 18th after a nightmare five-over-par round of 76 which included a triple bogey on the fourth hole.
It would take a special effort from the chasing pack to haul down Day, who is on the brink of becoming Australia's youngest-ever world number one at the age of 27.
The US PGA Championship winner recorded a birdie on the third hole at Conway Farms before he went bogey-birdie-birdie-bogey from the sixth to close the front nine.
It was a similarly mixed back nine for Day with shots gained at 12 and 14 and dropped on 13 and 15, although he finished with a flourish by birdieing the last.
Day was pleased to extend his overall lead, even if only by a single shot, as he felt the course conditions were a lot tougher than they had been during the first two rounds.
"It was very different. The wind was different - we had a northerly wind, which I think is a tougher wind," he told The Golf Channel.
"You are coming home with a lot of left-to-rights, coming-into-the-wind shots and they are difficult to always have.
"The pin locations were a little bit tougher today - I think the green speeds were a little quicker than I expected but overall I just wasn't quite as committed to my swing as I should have been. Hence when you have really difficult conditions like we have with that northerly wind it's very tough to commit to shots.
"I think overall with how I played today to shoot 69 was good to expand that lead by one shot was nice but I'm looking forward to a southerly wind tomorrow, I'm looking forward to getting some rest and hopefully I can pull it off."