Felix Auger-Aliassime and Jack Sock delivered for Team World at the Laver Cup, edging Team Europe's Matteo Berrettini and Andy Murray 2-6, 6-3, 10-8, here on Sunday.
Team Europe now leads Team World 8-7 with three matches to go. Each clash on Sunday is worth three points.
In an entertaining battle at the O2 in London, Auger-Aliassime and Sock held their nerve when it mattered, finding first serves and deep returns in the Match Tie-break to triumph after one hour and 37 minutes.
The American Sock has now won four points for his side, having teamed with Frances Tiafoe to defeat Roger Federer and Rafael Nadal in the Swiss star's final tour-level match on Friday night.
Auger-Aliassime will look to move Team World into the lead when he takes on former World No. 1 Novak Djokovic in the second match.
Captain Bjorn Borg is aiming to guide Team Europe to its fifth consecutive Laver Cup title against John McEnroe's Team World Sunday in the UK capital.
The three-day event started on Friday.