2021 Australian Open – Men's singles
Two-time defending champion Novak Djokovic defeated Daniil Medvedev in the final, 7–5, 6–2, 6–2 to win the men's singles tennis title at the 2021 Australian Open. It was his record-extending ninth Australian Open title and 18th major title overall. With his fourth-round win, Djokovic joined Roger Federer as only the second man to achieve 300 match wins in majors.
Aslan Karatsev was the first male qualifier to reach a major semifinal since Vladimir Voltchkov in the 2000 Wimbledon Championships, and the first at the Australian Open since Bob Giltinan in December 1977. Ranked world No. 114, he was the lowest-ranked player to reach a major semifinal since Goran Ivanišević at the 2001 Wimbledon Championships, the lowest ranked to do so at the Australian Open since Patrick McEnroe in 1991, and the first man in the Open Era to reach the semifinals on his major main-draw debut.
This was the first major in the Open Era to feature three Russian men in the quarterfinals, those being Medvedev, Karatsev, and Andrey Rublev.
This marked the first major main-draw appearance of future world No. 1 and seven-time major champion Carlos Alcaraz; he lost to Mikael Ymer in the second round. At 17 years old, Alcaraz was the youngest man to win a main-draw match at the Australian Open since Bernard Tomic in 2009.
Seeds
All seedings per ATP rankings.Seeded players
The following are the seeded players. Seedings are based on ATP rankings as of 1 February 2021. Rankings and points before are as of 8 February 2021.| Seed | Rank | Player | Points before | Points defending | Points won | Points after | Status |
| 1 | 1 | ''' Other entry informationPotential lucky losersWithdrawals† – not included on entry list‡ – withdrew from entry list before qualifying began @ – withdrew from entry list during qualifying Н – withdrew from entry list during a mandatory 14-day quarantine period § – withdrew from main draw |