Cameron Smith has blown a major chance to stay in touch with fellow Aussie Lucas Herbert at the Australian Open in a real Jekyll and Hyde performance.

Smith started the day two shots behind Herbert but was right in contention when he finished the first hole with an eagle.

The Queenslander would go on to hit three more birdies across the first nine holes at Kingston Heath but then everything changed.

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On the 10th, 12th and 15th holes, Smith hit bogeys and then a double bogey at the 16th.

He finished with two pars to be 6-under heading into the clubhouse, but now sits well behind Herbert who is 14-under overall.

His day started sensationally, hitting an eagle on the first and then two birdies.

Herbert’s only error was on the 10th when he hit a bogey before making up for it with three birdies on the 13th, 14th and 15th.

The biggest mover in the pack was Elvis Smylie who shot up 51 places into equal third.

The recent Australian PGA Championship winner hit nine birdies in his round to be 9-under overall.

“I felt like it was going to be pretty a bit tricky out here, I thought it was going to blow a bit more than it did but by the time we got around the back nine it started to show a bit of its teeth, Kingston Heath,” Smylie said post-round.

“… I’ve definitely catapulted myself up the leaderboard, which is nice and I’m looking forward to the weekend.”