Cameron Davis’ chances of a groundbreaking win in the US PGA Tour playoff event in Boston slipped away in the time that it took to play a few holes of the back nine today.

Davis, the talented, 25-year-old Seattle-based Sydney professional, began the third round of the $US9.5 million Northern Trust tied-second, just two shots from the lead held by former world No. 1 Dustin Johnson.

But the Australian shot a one-over par 72 today to slip to tied ninth. He is 10 shots back from the lead held by Johnson, who will jump to No. 1 in the world if he wins tomorrow, and whose 40-foot eagle at the 18th gave him a 64 and a five-shot buffer on the field.

It was a day that began with so much promise for Davis.

With three straight birdies to start the round today, he had the lead himself as Johnson and Scottie Scheffler in the final group made a slow start.

But Davis could not maintain his momentum. Still within two shots of Johnson after hitting his tee shot to four feet and making birdie at the 11th, the Australian lost his mojo.

Bogeys at the par-four 12th, where his chip from the left side of the green came back to his feet, and the 14th, where his drive was flared wide to another fairway, saw a change in his body language, with some frustration kicking in.

Then a disastrous triple bogey six at the par-three 16th compounded his issues. Davis’ tee shot only just carried the water in front of the green but spun back into the drink. From there, he his a poor wedge from the drop zone leaving himself a long putt for bogey, and he took three more shots to get down.

To his credit, he bounced back with a great birdie at the 17th after a pure iron shot beside the flag. But at 18 his second shot to the par five flared wide right and he needed to reload. Ultimately he scrapped out a par but it was not the day he was hoping for, nor the back nine (38 shots) that he needed.

Five of the six Australians playing in Boston this week are still on track to reach the BMW Championship in Chicago next week for the top-70 ranked players. The one who needs a low round tomorrow is Matt Jones, currently ranked outside the top 70.

Cameron Smith continued his nice form with a 66 today to sneak inside the top 20.

Davis was far from the only player to struggle. Rory McIlroy had two triple bogeys in his 74 and Tiger Woods limped to 73. Adam Scott had a 75. There are some very good players behind Davis, a point that his camp might well want to make to him overnight.

He has much to play for. Starting out the week 91st on the Fedex Cup points table, he needs to play well tomorrow to ensure that he gets to Chicago, currently projected as 65th and needing to stay inside the top 70.

That would give him a chance of getting to the Tour Championship in Atlanta which -- apart from all the richest at stake -- carries some significant exemptions for those who get there.

Davis will have half an eye on the majors, and his world ranking.

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