Adam Scott will take a three-shot lead into the final round of the Arnold Palmer Invitational on Sunday after a rollercoaster third day at Bay Hill.

Scott saw his seven-shot overnight advantage slashed to a single stroke after playing the first five holes in two over, but then rallied to lead by five with two holes remaining.

However, former US PGA champion Keegan Bradley then birdied the 18th to complete a superb 66 and Scott bogeyed the 17th to leave the destiny of the title – and with it the world number one ranking – in the balance.

“It was tough,” Scott told reporters. “I got off to a tough start and fought my way back all day. They don’t just hand you PGA titles after 36 holes.

“When you’ve got the lead you have to work for it. Everybody was making a run. I was battling but I’m in good shape for tomorrow.”

If Scott wins tomorrow and he and Tiger Woods do not play again before the Masters, Scott will assume top spot in the rankings before beginning his defence of the year's first Major.

A round of 71 left Scott on 15 under par, three ahead of Bradley and four clear of Jason Kokrak and Matt Every, Every's 66 the joint lowest score of the day.

Another American, rookie Chesson Hadley, was a shot further back on 10 under alongside Italy's Francesco Molinari, whose Ryder Cup team-mate Ian Poulter was seven off the lead on eight under par.

“I have been hitting the ball really nicely all week, all year really, but the last two days the putter has really gotten going which is a good sign,” said Bradley, who birdied six holes in a back nine of 31, including 16, 17 and 18.

“I was talking to Dr Bob (Rotella) and he told me to relax and not over-read putts, see it like you are a little kid and that’s the way I have been doing it.

“I know tomorrow I am going to have to go out there and shoot a really low score because Adam is one of the best players in the world but that’s what I live for. Tomorrow is one of the days you live for as a kid.”

Scott bogeyed the first after three-putting from long range and had to save par on the next after missing the green with his tee shot, while Hadley holed from 15 feet on the second and three feet on the fourth for birdie.

Hadley holed from 18 feet for another birdie on the fifth to close the gap further and when Scott bogeyed the same hole minutes later after hitting his approach over the green, that gap was down to just two shots.

And remarkably the lead was cut to just a single stroke when Hadley – winner of the Puerto Rico Open recently – got up and down from over the green on the par-five sixth hole for his fourth birdie of the day.

Hadley was unable to maintain the momentum however and dropped a shot on the seventh when he failed to get up and down from a greenside bunker, allowing Scott’s tap-in birdie on the sixth to take him three clear.

Further birdies on the 10th and 13th gave Scott a five-shot lead, and although he bogeyed the 14th, two more birdies on the 15th and 16th looked to be vital blows.

However, the 33-year-old failed to get up and down from the back of the 17th green and had to hole from six feet to avoid a bogey on the 18th for the third day running to give the chasing pack more than a little hope.

“I missed two par putts shorter than that,” Scott added. “To miss another would have opened the door a little bit too much for my liking.”

Graeme McDowell made four birdies over the final seven holes to card a five-under 67 and move to four under for the tournament and a tie for 19th.

Pádraig Harrington finished with a bogey on the 18th as he carded a one-over 73 and starts the final round in a share of 29th spot on three under.