Taylor Fritz held his nerve to beat Alexander Zverev and complete a 15-9 victory for Team World against Team Europe in the Laver Cup.
Team World led 12-9 going into the penultimate tie between the American and German.
With three points for a win, Zverev could have levelled the match, but Fritz won 6-3 7-6 (7-4) at the event in San Francisco.
He said the team environment and the encouragement of captain and compatriot Andre Agassi from courtside had inspired him to the title-clinching victory.
"We're going to have a fun night. We're definitely popping champagne in the locker room in a few minutes," said Fritz, who beat world number one Carlos Alcaraz on Saturday when Team World built a 9-3 overnight lead.