The 2021 AFC Champions League knockout stage was played from 13 September to 23 November 2021.[1] A total of 16 teams competed in the knockout stage to decide the champions of the 2021 AFC Champions League.[2]
The group winners and three best runners-up in the group stage from each region advanced to the round of 16, with both West Region (Groups A–E) and East Region (Groups F–J) having eight qualified teams.
| width=90 | Region | Group | width=220 | Winners | width=220 | Runners-up (best three from each region) |
|---|---|---|---|---|---|---|
| West Region | A | Istiklol | Al-Hilal | |||
| B | Sharjah | Tractor | ||||
| C | Esteghlal | — | ||||
| D | Al-Nassr | — | ||||
| E | Persepolis | Al-Wahda | ||||
| East Region | F | Ulsan Hyundai | BG Pathum United | |||
| G | Nagoya Grampus | Pohang Steelers | ||||
| H | Jeonbuk Hyundai Motors | — | ||||
| I | Kawasaki Frontale | Daegu FC | ||||
| J | Cerezo Osaka | — |
If two group winners played each other, the group winner marked with * hosted the match.[3]
| Qualified | 1A vs | 1B vs | 1C vs | 1D vs | 1E vs | |
|---|---|---|---|---|---|---|
| 2A/2B/2C | 1B* | 1A | 2A | 2B | 2C | |
| 2A/2B/2D | 1D | 2D | 2A | 1A* | 2B | |
| 2A/2B/2E | 1E | 2E | 2A | 2B | 1A* | |
| 2A/2C/2D | 1C* | 2D | 1A | 2A | 2C | |
| 2A/2C/2E | 2C | 2E | 1E* | 2A | 1C | |
| 2A/2D/2E | 2D | 2E | 2A | 1E* | 1D | |
| 2B/2C/2D | 2D | 1C* | 1B | 2B | 2C | |
| 2B/2C/2E | 2C | 1E | 2E | 2B | 1B* | |
| 2B/2D/2E | 2D | 1D* | 2E | 1B | 2B | |
| 2C/2D/2E | 2D | 2E | 1D* | 1C | 2C |
| Qualified | 1F vs | 1G vs | 1H vs | 1I vs | 1J vs | |
|---|---|---|---|---|---|---|
| 2F/2G/2H | 1G* | 1F | 2F | 2G | 2H | |
| 2F/2G/2I | 1I | 2I | 2F | 1F* | 2G | |
| 2F/2G/2J | 1J | 2J | 2F | 2G | 1F* | |
| 2F/2H/2I | 1H* | 2I | 1F | 2F | 2H | |
| 2F/2H/2J | 2H | 2J | 1J* | 2F | 1H | |
| 2F/2I/2J | 2I | 2J | 2F | 1J* | 1I | |
| 2G/2H/2I | 2I | 1H* | 1G | 2G | 2H | |
| 2G/2H/2J | 2H | 1J | 2J | 2G | 1G* | |
| 2G/2I/2J | 2I | 1I* | 2J | 1G | 2G | |
| 2H/2I/2J | 2I | 2J | 1I* | 1H | 2H |
In the knockout stage, the 16 teams played a single-elimination tournament, with the teams split into the two regions until the final. All ties were played as a single-leg match (Regulations Article 9.1).[4] Extra time and penalty shoot-out were used to decide the winners if necessary (Regulations Article 9.3 and 10.1).[2]
The schedule of each round was as follows.[1]
| Round | Date | |
|---|---|---|
| Round of 16 | 13–15 September 2021 | |
| Quarter-finals | 16–17 October 2021 | |
| Semi-finals | 19–20 October 2021 | |
| Final | 23 November 2021 |
The bracket of the knockout stage was determined as follows:
| Round | Format | |
|---|---|---|
| Round of 16 | Matchups within East region and West region decided by a series of permutations, based upon the three best runner-ups who qualified | |
| Quarter-finals | Matchups decided by a draw
| |
| Semi-finals |
| |
| Final |
|
The round of 16 was played over one leg, with the matchups determined by the combination tables based on which group runners-up qualified.|+West Region|}|+East Region|}
------------
------------
The quarter-finals were played over one leg, with the matchups and home team decided by draw held on 17 September at 15:00 (UTC+8) in Kuala Lumpur, Malaysia.
|+West Region|}|+East Region|}
----
----
The semi-finals were played over one leg.
|+West Region|}|+East Region|}
See main article: article and 2021 AFC Champions League final. The final was played over a single leg on 23 November. The host was determined on a rotational basis, with the match hosted by team from the West Region in odd-numbered years (Regulations 9.1.2).[2]