Big-serving Croat Ivo Karlovic became the first seed to fall at the Auckland Classic on Monday, losing in straight sets to Canada's Vasek Pospisil. (Ivo Karlovic, Martina Hingis Guide Hyderabad Aces to Win)
With the tournament's big names, including four-time champion David Ferrer, enjoying a first-round bye, the focus was on Karlovic as the only seeded player in action on day one of the Australian Open warm-up event.
But he failed to fire on centre court and Pospisil, ranked 16 places below the world number 23 ground out a 7-6 (7/4), 7-5 victory. (Richard Gasquet Survives Ivo Karlovic Ace Barrage)
"It feels great. I played really well and I'm thrilled about that," Pospisil said.
The Canadian's win sets up a second-round tie against his doubles partner Jack Sock of the United States who defeated Dominican Victor Estrella Burgos 6-0, 6-4.
American Donald Young eased past local wildcard Finn Tearney 6-2, 6-3.
"He played well and he had the crowd behind him, so he was tough to beat," Young said of his opponent.
Defending champion Jiri Vesely of the Czech Republic opens his campaign with a first-round clash against Spain's Roberto Bautista Agut on Tuesday.
Ferrer, who is chasing a record-breaking fifth title in Auckland, will not play until Wednesday.
Frenchman Jo-Wilfried Tsonga, American two-time champion John Isner and South Africa's Kevin Anderson will also go straight into the second round.
Meanwhile, Germany's Phillip Kohlschreiber, the 2008 champion now ranked 35 in the world, looms as a dark horse in the draw.