Fabian Marozsan held his nerve to beat veteran Gael Monfils in three sets on the opening day of the Auckland Classic on Monday and set up a clash with top seed Ben Shelton.
Ahead of the Australian Open, the 61st-ranked Marozsan outlasted the 37-year-old Frenchman 6-4, 6-7 (6/8), 7-6 (7/4).
The 24-year-old Hungarian, who produced a stunning win over world No 2 Carlos Alcaraz last year in Rome, said: "I'm happy to beat Monfils, he's a great player.
"He was a top-10 player in the last 15 years so he has great experience."
Monfils, spurred on by the crowd chanting his name, looked exhausted in the closing stages of the two-hour, 35-minute marathon as he leaned on either his racket or a sideline chair between points.
Marozsan will face world number 15 Shelton in round two.
The American is coming off a first-round exit in Brisbane and will be keen to get game time under his belt before heading to the first Grand Slam of the year starting on Sunday.
In an upset, Botic van de Zandschulp from the Netherlands defeated fifth seed Chris Eubanks, who struggled with a back injury, 7-6 (7/5), 6-2.