American Jack Sock has pulled off the biggest upset at the Auckland tennis classic, knocking out second-seeded German Tommy Haas.

Sock served well throughout the 6-4 6-4 second-round victory against world No.12 Haas, who was playing his first match of the year.

Haas looked rusty after a first-round bye and will play next week’s Australian Open with the benefit of just one match.

But the 35-year-old German says he made the right decision not to play in Perth a week earlier.

“I have a family now. I didn’t want to leave Christmas Eve; I wanted to stay home,” he said.

“The season is long, and that’s a problem with tennis – it starts too early, and it ends too late. You have to pick the right battles for yourself.”

Sock will play Roberto Bautista Agut in the quarter-finals, with the Spaniard knocking out sixth seed Benoit Paire of France 6-3 6-4.

The news was better for German No.2 Philipp Kohlschreiber, who beat Horacio Zeballos of Argentina 6-4 6-2.

Kohlschreiber was taken to three sets on Tuesday by Pablo Carreno Busta but was much happier with his efforts on Wednesday.

“I played a great match. I think not many mistakes, I served well and very clever with the wind.

“Yesterday maybe I wasn’t feeling that great after the match, but today it was almost a perfect match.”

Earlier, ninth seed Daniel Brands and wildcard Marcos Baghdatis were beaten in first-round matches by two Americans who didn’t make the original draw.

Brands was downed 7-5 4-6 6-3 by Bradley Klahn in a match carried over from Tuesday after rain ended the evening session early, while Baghdatis – the 2006 Australian Open finalist – lost 7-5 6-7 (7-9) 6-4 to Steve Johnson.