World number one Jordan Spieth believes his best is yet to come at the Australian Open after a second round of 68 left him four shots off the lead held by home player Matt Jones.

Added to a first-round 71, Friday's performance left Spieth on three under par and the 22-year-old American fancies his chances for the remainder of the tournament at The Australian in Sydney.

Defending champion Spieth told the tournament website: "I feel like I've still got the best golf yet, to be played. That's what's positive. That's what I'm going with.''

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Spieth had struggled in the windy conditions on the opening day but found the calmer skies more to his liking on day two and that was reflected in his score.

Five birdies and two bogeys kept Spieth in touch with Jones who had set the clubhouse target earlier in the day.

Despite the winds being lighter, Spieth suggested the conditions still presented a challenge because of their changing direction.

He said: "It's not local knowledge or anything. Today it started at east-south-east and then it worked its way to east-north-east and you're trying to figure out when that's actually happening. It makes a huge difference.

"It's nothing we haven't seen before; it's just typically you don't see this much crosswind on golf courses. Today there was only a couple of holes – maybe one and two and one on the back nine – that wasn't straight sideways.''

Behind Jones lies fellow Australian Todd Sinnott on four under, before a group of five players including Spieth a shot further back.

That group includes Belgian Nicolas Colsaerts and Australians Geoff Ogilvy, Aron Price and Lincoln Tighe. Northern Ireland's Darren Clarke and England's Lee Westwood are in a tie for 14th place on even par.