Casper Ruud defeated John Isner 6-7, 7-6, 7-5 to help Norway upset the United States on the first day of the 2020 ATP Cup.
Ruud saved two match points in the second set and weathered 33 aces from Isner.
Taylor Fritz thrashed Viktor Durasovic 6-2, 6-2 in the opening match in Perth.
Ruud then backed up in the decisive doubles alongside Durasovic to down Rajeev Ram and Austin Krajicek 4-6, 6-3, 10-5.
"I didn't have much time to recover from my singles," Ruud said. "I was a little bit low (on energy) but I got the feet going and we played great. The players are super proud to beat the US."
Ruud, whose father Christian is Norway's captain, clawed back into the singles match and stormed out to a 6-4 lead in the second set tiebreak, but was thwarted on his set points by a desperate Isner.
He saved two match points in a see-sawing set before finally converting on his fifth attempt to keep Norway alive.
It appeared the match was going the distance in the third set until an inspired Ruud broke in the 12th game to clinch his first victory over a top-20 ranked player.
Earlier, Fritz gave heavily favoured United States the perfect start with a commanding victory over Durasovic in 61 minutes.
"For the first match of the year, I played really well," he said. "Last year was my breakthrough, but I always put pressure on myself to do well."
Fritz unleashed his big serve with 11 aces and returned accurately to underline the gulf in rankings.
The match was played under the roof due to unusually cool and damp morning conditions in Perth.
Info and photo by AFP Photo/TONY ASHBY
