Team Europe are on track for their fourth consecutive Laver Cup triumph after earning an early 3-1 lead against Team World.
Opening-day honours went to Bjorn Borg's Team Europe at TD Garden in Boston, where the defending champions moved into the box seat thanks to wins for Andrey Rublev, Matteo Berrettini and Casper Ruud in the singles on Friday.
John Isner and Denis Shapovalov managed to get Team World on the board in the evening's final doubles match against Alexander Zverev and Berrettini 4-6 7-6 (7-2) 10-1.
Roger Federer and Rod Laver were in the crowd as Team Europe – headlined by newly crowned US Open champion Daniil Medvedev and consisting of six of the world's top 10 – made a strong start courtesy of Norwegian Ruud, who overcame Reilly Opelka 6-3 7-6 (7-4), improving his career record to 3-0 against the towering American, and beating him in straight sets for the first time.
Italian star Berrettini then overcame Team World's Felix Auger-Aliassime 6-7 (3-7) 7-5 10-8 in the competition's longest match at two hours, 52 minutes.
Berrettini escaped with the second set after facing two break points in the penultimate game before prevailing against the Canadian in a thrilling match tie-break.
"One of the best matches bar none that I've ever seen played, absolutely just enthralling," said captain John McEnroe, whose Team World are eyeing their first Laver Cup trophy.
Rublev rallied past Argentina's Diego Schwartzman, who won the opening set and led 6-2 and 8-5 in the match tie-break before losing 4-6 6-3 11-9.
"Today we are a bit more lucky; Matteo won a tough match against Felix in a super tiebreak, now you saw my match," said Russian star Rublev.
"It was so close; Diego was leading all the super tiebreak, but in the end I find a way to win.
"This happens. This is tennis, this is sport. It’s emotions. Someone has to win, someone has to lose."
On day two, Stefanos Tsitsipas and Zverev headline the day session against Team World's Nick Kyrgios and Isner.
In the evening, Medvedev will meet Shapovalov before Rublev and Tsitsipas team up for a doubles battle with Kyrgios and Isner.