Matthew Barton pulled off the shock result of the day to eliminate Steve Johnson and set up a second-round clash with top seed David Ferrer at the ASB Classic.
The Australian 24-year-old is ranked 299th in the world, but overcame his American opponent - ranked 267 places higher - in a 6-3 3-6 6-3 victory.
Barton hit 13 aces and saved five of six break points, including a set point for Johnson in the first, to earn his first main-draw win on the ATP Tour.
And it proved to be a day of upsets in Auckland, as Jack Sock brushed Victor Estrella Burgos aside 6-0 6-4 in just 49 minutes, while Vasek Pospisil got the better of seventh seed Ivo Karlovic.
Pospisil won a closely fought encounter 7-6 (7-4) 7-5 to set up a second-round clash with doubles partner Sock.
World number 100 Thiemo de Bakker sprung a surprise to see off Albert Ramos 6-3 6-4, but Donald Young faced little resistance as he breezed past main-draw debutant Finn Tearney 6-2 6-3.
In the day's remaining match, qualifier Robin Haase triumphed 6-4 6-1 against Pablo Andujar.