Nick Kyrgios has led the World team to its only success on the opening day of the Laver Cup, teaming with American Jack Sock to beat Europe's Rafael Nadal and Tomas Berdych.
Marin Cilic, Dominic Thiem and Alexander Zverev handed Europe the lead on Friday, with Bjorn Borg's team holding a 3-1 lead over the World at the end of day one in Prague.
Kyrgios and Sock beat Nadal and Berdych 6-3 6-7 1-0 (10-7).
Under the new Laver Cup format, matches are best of three sets. In the event of split sets, the third set is be a 10-point match tiebreaker.
"The first set they were better than us, but later it was close. We started to return more and be more aggressive," Nadal said.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"I am just happy the way the day went... happy to go to bed 3-1."
Earlier, Cilic defeated World's late call-up Frances Tiafoe 7-6 7-6, while Austrian Thiem tacked on a second point for Europe as he rallied to beat John Isner 6-7 7-6 1-0 (10-7).
And German world number four Zverev scraped through on his fifth match point against Canadian breakout player Denis Shapovalov 7-6 7-6.
World number two Roger Federer sat out the opening day in a likely strategic move by Borg.
On hand for the event is Rod Laver, the Australian tennis icon who was the last man to win the calendar-year grand slam in 1969.
Borg and World skipper John McEnroe, rivals in the 1970s and 1980s, have thrown their support behind the event, despite some fears it could take away from the Davis Cup, whose congested format has been criticised for years by players.
"I'm hopeful that this is going to be successful and force some people to take a good, hard look at the rest of the schedule. With Davis Cup they need to make some changes," McEnroe said.
