Donskoy, seeded 30th in the first round, outplayed the Indian Ramkumar Ramanathan with a score of 4: 6, 7: 6 (7: 1), 6: 4.
The game lasted 2 hours and 35 minutes.
In the next round, the Russian will play with Romanian Mariusz Kopil.
US Open - 2021 will be held from August 30 to September 12 in New York.
Earlier it was reported that Kasatkina reached the quarterfinals of the tennis tournament in Cleveland.