Team Europe's Medvedev beat Novak Djokovic in the US Open finalTeam Europe closed in on victory in the Laver Cup after building a commanding 11-1 lead over Team World in Boston.
Stefanos Tsitsipas, Alexander Zverev and US Open champion Daniil Medvedev won their singles matches to extend Team Europe's lead from 3-1 to 9-1.
Andrey Rublev and Tsitsipas then claimed victory in their doubles match as Team World failed to register a win on the second day.
Team Europe need one win on Sunday to retain the Laver Cup.
The contest is the fourth edition of the event, which sees six men's players from Team Europe and Team World play a series of singles and doubles matches.
The three-day event sees one point awarded for a victory on day one, two for wins on day two and three on the final day.
Greece's Tsitsipas beat Australian Nick Kyrgios 6-3 6-4 at the start of day two before Germany's Zverev overcame American John Isner 7-6 (7-5) 6-7 (6-8) 10-5 following a third-set tie-break.
Russian Medvedev comfortably beat Canada's Denis Shapovalov 6-4 6-0 while Rublev and Tsitsipas also needed a match tie-break to beat Isner and Kyrgios 6-7 (8-10) 6-3 10-4.
"I played unbelievably, especially the second set," said Medvedev.
"I didn't know what to expect because after the US Open, I didn't play for a week and a half. [I] came here, practised as much as I could the past three days, so I didn't hit many balls, but was surprisingly feeling well."
Europe, captained by Bjorn Borg, have won all three previous editions of the competition, while Team World are led by John McEnroe.
