Unheralded German Peter Gojowczyk has rocked the ASB Classic in Auckland, eliminating top seed and defending champion Jack Sock.

Gojowczyk, a journeyman ranked 65th in the world, tipped over Sock 6-3 6-3 in Wednesday’s second-round action, dominating from first to last.

Sock had earned a bye to the second round due to his seeding, but looked well off his world No.8 ranking and last year’s ATP World Tour Masters triumph.

He made unforced error after unforced error against Gojowczyk, who served the house down with nine aces and won 88 per cent of first-serve points.

He’ll face Robin Haase in the quarter-finals after the veteran Dutchman defeated Classic lucky loser Lukas Lacko 7-6 (7-4) 6-3 in just under 90 minutes.

Sock – a recent Hopman Cup contender – started well enough in front of a bumper crowd, overcoming touches of rustiness to break early.

But Gojowczyk roared back, breaking twice in succession and serving out the first set 6-3 before he was gifted victory by Sock’s carelessness.

He’ll need genuine improvement to stake a claim for the Australian Open later this month, while Gojowczyk can dream of a second ATP title in Auckland.

He also won a tournament in Metz last year.

Earlier, Spaniard Roberto Bautista Agut rolled over the top of a fast-fading Steve Johnson, winning his second-round tussle 2-6 6-2 6-1.

Blitzed by Johnson’s powerful service game, the fifth seed and 2016 Classic champion struggled early and lost the first set but duly wrested back control.

His precision came to the fore in the second set, winning almost 80 per cent of his first-serve points, before an equally clinical showing in the decider.