| Champ: | Boris Becker |
| Runner: | Ivan Lendl |
| Score: | 1–6, 6–4, 6–4, 6–4 |
| Draw: | 128 |
| Seeds: | 16 |
See main article: 1991 Australian Open.
Boris Becker defeated the two-time defending champion Ivan Lendl in the final, 1–6, 6–4, 6–4, 6–4 to win the men's singles tennis title at the 1991 Australian Open.[1] [2] It was his first Australian Open title and fifth major singles title overall.
See also: 1 and 1. 
Stefan Edberg (semifinals)
See also: 2 and 8. Boris Becker (champion)
See also: 3 and 3. Ivan Lendl (final)
See also: 4. 
Pete Sampras (withdrew because of shin splints)[3]
See also: 5 and 4. Goran Ivanišević (third round)
See also: 6 and 5. 
Emilio Sánchez (first round)
See also: 7 and 2. Brad Gilbert (third round)
See also: 8 and 7. Jonas Svensson (third round)
See also: 9 and 2. Andrei Chesnokov (first round)
See also: 10 and 7. 
Guy Forget (quarterfinals)
See also: 11 and 4. Jakob Hlasek (first round)
See also: 12 and 5. Jay Berger (third round)
See also: 13 and 3. Aaron Krickstein (fourth round)
See also: 14 and 6. Andrei Cherkasov (second round)
See also: 15 and 8. Marc Rosset (first round)
See also: 16 and 1. Jim Courier (fourth round)
See main article: 1991 Australian Open – Men's singles qualifying.
a. Andre Agassi (No. 4), Andrés Gómez (No. 6), Thomas Muster (No. 7), John McEnroe (No. 13), Guillermo Pérez Roldán (No. 14), Michael Chang (No. 15) and Juan Aguilera (No. 19) all withdrew from the tournament prior to the seedings.