Englishman Justin Rose sits well clear of the field after the third round of the US PGA Tour BMW Championship but Australians John Senden and Geoff Ogilvy are ready to pounce.

The third of four play-off events became Rose's tournament to lose after he moved to 13-under-par 200, gaining a four-shot lead over Senden who sits alone in second place at nine under.

With one round to play Ogilvy sits at eight under in a tie for third place with American Bill Haas, putting the Victorian in the box seat for a spot in the Presidents Cup and Tour Championship.

Both Senden (top four) and Ogilvy (top three) need a high finish to make the lucrative Tour Championship in Atlanta.

To be part of Greg Norman's International team for the Presidents Cup Senden needs a win and Ogilvy needs a top 20 if Senden fails to win, or a top five if his countryman is victorious.

The 40-year-old Senden had a disastrous start on Saturday with three bogeys in his opening five holes.

The Queenslander missed two one-metre putts during the horror stretch, one to save par and another to claim what would have been a timely birdie on the third hole.

Rather than throw in the towel he ground out five straight pars before starting his resurrection.

Making amends on the back nine, Senden made clutch birdies on the 11th, 14th, 15th and 18th holes.

The round started promising for Ogilvy when he nailed a 4-metre, birdie putt on the opening hole but any momentum he thought he'd gained was washed away on his next swing.

The Victorian pulled his iron shot well left on the par-three second hole and ended up with a bogey before dropping another shot on the third.

On the par-five 11th, the 33-year-old powered in an 8-metre, birdie putt before adding back-to-back birdies on the 13th and 14th holes with some precision iron play to close range.

He made it three in a row and four from five holes when he reached the par five 15th in two and comfortably two-putted to get to eight under.

Ogilvy confirmed the long putt on the 11th gave his round some much-needed impetus.

"A 25-footer, that's a real bonus," he said.

"I knew it was hard out there so it's a pretty good to finish the last nine holes with four birdies."

Robert Allenby's quest for a place in the Presidents Cup team and the Tour Championship faded when two double bogeys in the last three holes dropped him to two-under in a tie for 17th.

Jason Day finished at two-over 215 while Marc Leishman was a shot further back at three over 216.

Aaron Baddeley's hopes of automatically qualifying for the Cup appear over after he fell back to four-over 217 in a tie for 46th and, should he fall further back on Sunday, he'll miss the Tour Championship.

Adam Scott also finished at four-over 217 although his place in both the Presidents Cup and Tour Championship is already secured.