Australian qualifier Matthew Barton says a bit of luck went a long way in his upset of world No.32 Steve Johnson at the ASB Classic.

Twenty-four-year-old Barton, ranked 299 in the world, beat the American 6-3 3-6 6-3 on opening day in Auckland.

He took a commanding lead after five games in the first set, carried by a consistently strong serve, including 13 aces for the game.

Johnson, who has made the quarter-finals in Auckland the past two years, was visibly frustrated as unforced errors began to pile up towards to the end of the first set.

Backed by the Auckland crowd the Aussie pulled out numerous shots from the baseline that were a combination of well-picked and occasionally fortunate.

Barton will now face tournament top seed and world No.7 David Ferrer in the next round.

He described the win as an “unreal experience”.

“I got lucky really. I got some lucky returns but I was working, really focusing on those big points,” he said.

He said Johnson would rate among his toughest opponents to date and the gap in quality was tangible.

In the day’s other match-ups, American Jack Sock, 23, quickly dispatched Dominican Victor Estrella Burgos, 35, 6-0 6-4.

Sock, No.126 in the world and who made the quarter-finals in Auckland 2014, swept to victory in just 49 minutes.

While the first set was a one-sided affair, Estrella Burgos, world No.156, looked more lively in the second, pushing Sock to 5-4.

But it was not his day: picking up six double faults and troubled by unforced errors, he struggled to get win a break against the agile Sock.

Earlier, New Zealand No.1 Finn Tearney made a swift exit from the Classic, losing in 6-2 6-3 to world No.48 American Donald Young.

Tearney had a stellar run last in the ATP year, rising more than 1000 ranks to reach his current world ranking of 363.

His loss leaves wild card Michael Venus as the only New Zealander remaining in the tournament.