World No.1 Rory McIlroy has yet to find his groove midway through his first round in cool and overcast conditions at the Australian Open in Sydney.

After teeing off on the 10th, McIlroy reached the turn at even par after notching just one birdie in the first nine holes of his title defence at The Australian.

Richard Green, Brett Rumford and Aron Price were setting the early pace at three-under, while 15 players were in red figures early in their opening rounds.

After missing a three-metre birdie attempt at the 12th, McIlroy needed to get up and down after overhitting his approach on the next hole to stay level with the card.

He grabbed his first birdie of the day at the short par-5 14th, splashing his bunker shot to inside a metre and converting.

But he handed the shot straight back when unable to save par from the trap on the par-3 15th.

The Northern Irishman crunched a booming drive down the 17th, only to block his approach shot and scramble to make par and he was unable to birdie the par-5 18th.

McIlroy is playing alongside former champion Geoff Ogilvy and Matt Jones, a career-long member of The Australian, which was recently revamped by Jack Nicklaus.

Having staged a memorable final-day battle with Adam Scott to win the Stonehaven Cup last year, he cautioned fans shouldn’t expect a two-way duel this time around.

“There’s a lot of good players, a lot of good Australians are playing,” McIlroy said after Wednesday’s pro-am.

“Jordan Spieth’s obviously here, I’m playing with Matt Jones and this is basically his home golf course, so he’s going to have a good shot at it.

“But it’s a strong field. It’s definitely not a two-horse race.”

Scott opens his championship quest just after midday AEST alongside Spieth and newly-crowned Australian Masters champion Nick Cullen.

“I haven’t played here that much in the past. Obviously there’s been a lot of work done and they’ve presented a beautiful golf course for us this week,” world No.3 Scott.

“My feeling is it’s certainly going to favour the longer hitters this week. There’s no rough out there.

“It seems like it just hasn’t grown in for them yet but hopefully with some pretty long straight driving, I’ll be able to take advantage of a few holes.

“The wind is the definitive this week. With no rough, so that’s not going to penalise any stray shots as much as it normally would, but the winds still will.”