Australian Open, but was knocked out by Frances Tiafoe in four sets. Having suffered from a shoulder injury, Dimitrov returned to play in the Miami Masters, reaching the third round. Dimitrov then started his clay court campaign at the Monte-Carlo Masters, where he lost to Rafael Nadal in the third round. Dimitrov then went to the third round of Barcelona Open. His ranking deteriorated to No. 49, the lowest since 2012. At the French Open, Dimitrov upset Marin Čilić in the second round but was subsequently eliminated by Stan Wawrinka in straight sets. Dimitrov had a disappointing Wimbledon, losing to Corentin Moutet in five sets in the first round, despite being up two sets. Dimitrov's hard court season started off poorly. He lost in the first round of the Atlanta Open to world No. 405 Kevin King, who had never won a main-draw match on the ATP Tour. Dimitrov then lost to Stan Wawrinka in the first rounds of both the Rogers Cup and the Western & Southern Open. Following this, Dimitrov had lost seven of his past eight matches, and his ranking had slipped to No. 78, his lowest ranking in over seven years. At the US Open, Dimitrov was unseeded. He defeated Andreas Seppi in the first round before receiving a walkover over 12th seed Borna Ćorić. He then defeated lucky loser Kamil Majchrzak and Alex de Minaur in straight sets to reach the quarterfinals. There, he faced third seed Roger Federer. In a lengthy five-set match, Dimitrov upset Federer to reach his first Grand Slam semifinal since the 2017 Australian Open. This was also his first career win against Federer, having been defeated on seven previous occasions. He then lost to Daniil Medvedev in the semifinals. As a result of this run, Dimitrov rose 53 ranking places in a single tournament, appearing at World No. 25 the next week. Dimitrov failed to proceed beyond the second round at Chengdu, Beijing, Stockholm, and Vienna. At the Paris Masters, he defeated Ugo Humbert and 12th seed David Goffin to reach the third round, where he defeated the fifth seed Dominic Thiem. In the quarterfinals, he defeated Cristian Garín, before losing to Djokovic in straight sets in the semifinals. 2020: Inaugural ATP Cup captain, French Open fourth round In January, Dimitrov participated and led as captain the Bulgarian team in the inaugural 2020 ATP Cup where the top 24 countries