qualified based on the singles ATP ranking of their No. 1 country player. The Bulgarian team was No. 19 based on Dimitrov's ranking and part of Group C where Dimitrov won both his single matches against the top players of Great Britain Dan Evans and Moldova Radu Albot. He pulled a victory in doubles where as the underdogs he and teammate Alexandar Lazarov stunned the top British experienced pair of Jamie Murray/Joe Salisbury in a close three sets match. In October, Dimitrov reached the fourth round of the French Open for the first time, defeating Roberto Carballes Baena, where he lost to Stefanos Tsitsipas in straight sets. He finished the year in the top 20 for the fifth year in a row, ranked World No. 19. 2021: Australian Open quarterfinal, Indian Wells semifinal In February, Dimitrov seeded 18th reached his fourth quarterfinal at the 2021 Australian Open (AO), defeating former Grand Slam champion Marin Cilic in the first round, Alex Bolt, 15th seed Pablo Carreno Busta by retirement and 3rd seed and the previous year's runner-up Dominic Thiem in the fourth round, before losing to qualifier Aslan Karatsev after suffering from back spasms. Dimitrov retired in the first round of the French Open against Marcos Giron for the same reasons as a result of his back problems, after failing to convert three match points in the third set. Seeded 18th at the 2021 Wimbledon Championships he lost to Alexander Bublik in the second round in three straight sets with two tiebreaks after Bublik hit 34 aces against Dimitrov. He took his revenge by defeating Bublik at the 2021 Western & Southern Open Masters in Cincinnati to reach the round of 16. He lost to Daniil Medvedev in straight sets. At the US Open, he retired with a foot injury after losing the first two sets to Alexei Popyrin in the second round. He dropped out of the Top 25, since he could not defend his points from the 2019 US Open semifinal, to No. 29 on 13 September 2021. In late September, Dimitrov recorded his first win over Marton Fucsovics in three ATP Head2Head meetings at the 2021 San Diego Open to reach the second round. He then won in the second round defeating ATP debutant and lucky loser August Holmgren (tennis), after Felix Auger-Aliassime withdrawal, in straight sets 6–1, 6–1 in a 56 minutes match to reach his fifth