Roger Federer and John Isner won their Laver Cup singles matches as Team Europe lead Team World 5-3 after day two of the event.
Nick Kyrgios had overcome a 0-4 deficit in the first-set tie-break to take the opening set in Geneva, Switzerland.
But Federer fought back from two games down in the match tie-break to defeat the Greek 7-6 (7-5) 5-7 10-7.
Federer maintained his unbeaten run in Laver Cup singles matches with a 5-0 record.
Kyrgios won a spectacular 31-stroke rally with a backhand winner early in the game which saw him claim the opening set, but a weak service game from the Greek at 5-5 in the second set gave the world number three the advantage.