Seventh seed Ivo Karlovic was the most notable casualty as the ASB Classic began in Auckland on Monday.
The Croatian was beaten 7-6 (7/4) 7-5 by Canada's Vasek Pospisil, with the only break of serve coming in Karlovic's final service game.
With Karlovic the only seed in action, the stage was left to qualifiers led by Dutch pair Thiemo de Bakker and Robin Haase.
Both players saw off Spanish opponents, Haase a 6-4 6-1 winner over Pablo Andujar while De Bakker beat Albert Ramos-Vinolas 6-3 6-4. Australia's Matthew Barton won 6-3 3-6 6-3 against American Steve Johnson.
Jack Sock triumphed 6-0 6-4 against Victor Estrella Burgos and was joined in round two by fellow American Donald Young, who beat Australian wild card Finn Tearney 6-2 6-3.
Source: PA
