Jordan Spieth is threatening to run away with the Stonehaven Cup after claiming a three-stroke lead midway through the final round of the Australian Open.

The American drawcard birdied four of his first nine holes, including three in a row from the fifth, to charge to nine-under-par for the championship.

Fellow third-round co-leader Brett Rumford is Spieth’s nearest pursuer at six under after picking up one shot on the front nine, with Greg Chalmers a further stroke behind in outright third.

After grabbing a share of the lead with a birdie on the first hole, Adam Scott has fallen five shots off the pace, while world No.1 Rory McIlroy continues to go backwards in his title defence.

McIlroy is two over for his round and three over for the tournament, a distant 12 strokes behind Spieth.

After a horror front-nine five-over-par 40 on Thursday, Scott had all the momentum after clawing his way into the lead on Sunday.

But after taking a bogey on the tough par-3 fourth, when he was unable to save par from the greenside trap, Scott found his championship hopes slipping away after making a meal of the par-5 fifth.

The world No.3 had to take a penalty drop for an unplayable lie after blocking his tee shot into jungle and then hooked backed into trees on the left.

He punched out through a narrow opening but was unable to get up and down, the nasty double-bogey leaving Scott five behind Spieth at that point.

Despite a birdie on the sixth, Scott remained five adrift of the 2014 Masters runner-up in his quest for a second national championship.