2021 AFC Cup knockout stage
The 2021 AFC Cup knockout stage was played from 25 August to 5 November 2021. A total of 8 teams competed in the knockout stage to decide the champions of the 2021 AFC Cup. Teams from ASEAN Zone did not compete in the knockout stage, due to the cancellation of group stage matches in ASEAN Zone.
Qualified teams
The following teams advanced from the group stage:- The winners of each of the three groups and the best runners-up in the West Asia Zone advanced to the [|Zonal semi-finals].
- The winners of each group in the South Asia Zone, and the East Asia Zone advanced to the [|Inter-zone play-off semi-finals].
- The winners of each group in the Central Asia Zone advanced to the [|Zonal finals].
| Key to colours |
| Teams which enter the [|Inter-zone play-off finals] |
| Teams which enter the Inter-zone play-off semi-finals |
| Teams which enter the Zonal finals |
| Teams which enter the Zonal semi-finals |
| Zone | Group | Winners | Best runners-up |
| West Asia Zone | A | Al-Ahed | Al-Salt |
| West Asia Zone | B | Al-Muharraq | Al-Salt |
| West Asia Zone | C | Al-Kuwait | Al-Salt |
| South Asia Zone | D | ATK Mohun Bagan | — |
| Central Asia Zone | E | Ahal | — |
| Central Asia Zone | F | Nasaf | — |
| East Asia Zone | J | Lee Man | — |
Format
In the knockout stage, the eight teams played a single-elimination tournament. Each tie was played as a single match. Extra time and penalty shoot-out were used to decide the winners if necessary.
Schedule
The schedule of each round is as follows. Matches in the West Asia Zone will be played on Mondays and Tuesdays, while matches in the Central Zone and the Inter-zone play-offs will be played on Tuesdays and Wednesdays.| Round | Date |
| Zonal semi-finals | 20–21 September 2021 |
| Zonal finals | 25 August 2021, 20 October 2021 |
| Inter-zone play-off semi-finals | 21–22 September 2021 |
| Inter-zone play-off final | 20 October 2021 |
| Final | 5 November 2021 |
Bracket
The bracket of the knockout stage was determined as follows:| Round | Matchups |
| Zonal semi-finals | ;West Asia Zone
|
| Zonal finals | ;West Asia Zone
|
| Inter-zone play-off semi-finals |
|
| Inter-zone play-off finals |
|
| Final |
Zonal semi-finals
Summary
The West Asia Zonal semi-finals were played over one leg, with the home team determined by the draw mechanism based on which group runners-up qualify. A group winner hosted the match against a group runner-up. If two group winners played each other, one of the group winner hosted the match.
West Asia Zone
----Zonal finals
Summary
The West Asia and Central Asia Zonal final were played over one leg, with the home team decided by draw. The winners of the West Asia Zonal final advanced to the final, while the winners of the Central Asia Zonal final advanced to the Inter-zone play-off semi-finals.
Inter-zone play-off semi-finals
Summary
After matches in ASEAN Zone was cancelled, there were only three teams which qualified to the Inter-zone play-off semi-finals, i.e., the winners of the South Asia Zone, the winners of the East Asia Zone, and the winners of the Central Zonal final. The three Zonal champions were drawn into two pairings where one club got a bye to the Inter-zone play-off final, which happened for Lee Man. The matchups and order of legs decided by draw, without any seeding with the winner of Central Zonal Final hosting the match and the winner of South Asia Zone being the away team.
Inter-zone play-off final
Summary
In the Inter-zone play-off final, the two teams which advanced from the Inter-zone play-off semi-finals played each other, with the order of legs determined by the Inter-zone play-off semi-final draw. The winners of the Inter-zone play-off final advanced to the final.
Final
The final was played over one leg, between the winners of the West Asia Zonal final and the winners of the Inter-zone play-off final. The home team was determined on a rotation basis, with the match hosted by the winners of the West Asia Zonal final, as in the case of odd-numbered years.