Rafael Nadal and Roger Federer joined forces to win the doubles in the new Laver Cup on Saturday.
They teamed up for the first time to defeat Sam Querrey and Jack Sock 6-4, 1-6, 10-5 in the team event between Europe and the rest of the world.
"We will always forever be rivals as long as we are active. And after this we will be rivals again," said Federer, ranked number two in the world and holder of 19 career grand slam titles to top-ranked Nadal's 16.
"But this was something very special. Knowing you can trust him in the big moments, seeing his decision-making, seeing his thought process, it was very interesting."
"It was definitely a different day to other days in my life," he added.
The doubles victory put Team Europe up 9-3 going into the final day when the four matches are each worth three points.
"It was unbelievable," Nadal said.
Earlier in the day, team Europe almost completed a sweep in singles action.
Nadal was victorious over Sock 6-3, 3-6, 11-9 and Federer dispatched Querrey 6-4, 6-2.
The lone victory for team World came from Nick Krygios who defeated the host nation's Tomas Berdych 4-6, 7-6(4), 10-6 to claim their lone two points of the day.
The inaugural Laver Cup is at Prague's O2 Arena on an unusual black hard court.
Alexander Zverev, Marin Cilic, and Dominic Thiem also form the European team, while John Isner, Denis Shapovalov and Frances Tiafoe play for the world. Europe needs two more victories from Sunday's four games to win.