USTA spokesman Chris Widmaier said that the exclusion of Guido Pella and Hugo Dellien was in line with advice from the Centers for Disease Control and Prevention.

Novak Djokovic lost serve five times in a 6-3, 4-6, 6-2 defeat by Russia's 10th seed Daniil Medvedev.

Marin Cilic suffered a shock Wimbledon second round exit as last year's runner-up blew a two-set lead in his 3-6, 1-6, 6-4, 7-6 (7/3), 7-5 loss to Argentina's Guido Pella on Thursday.

Defending champion Marin Cilic defeated Argentine qualifier Guido Pella 6-3, 7-6 (7/3), 7-6 (7/3).

Djokovic has won every Grand Slam title except the French Open and has made this year's tournament his priority. The Serb lost last year's rain-interrupted final at Roland Garros to Spaniard Rafael Nadal.