The 2018 AFC Champions League knockout stage was played from 7 May to 10 November 2018.[1] A total of 16 teams competed in the knockout stage to decide the champions of the 2018 AFC Champions League.[2]
The winners and runners-up of each of the eight groups in the group stage advanced to the round of 16, with both West Region (Groups A–D) and East Region (Groups E–H) having eight qualified teams.
| width=90 | Region | Group | width=210 | Winners | width=210 | Runners-up |
|---|---|---|---|---|---|---|
| West Region | A | Al-Ahli | Al-Jazira | |||
| B |  Al-Duhail |  Zob Ahan | ||||
| C | Persepolis | Al-Sadd | ||||
| D | Esteghlal | Al-Ain | ||||
| East Region | E |  Jeonbuk Hyundai Motors |  Tianjin Quanjian | |||
| F | Shanghai SIPG | Ulsan Hyundai | ||||
| G | Guangzhou Evergrande |  Buriram United | ||||
| H | Suwon Samsung Bluewings |  Kashima Antlers |
In the knockout stage, the 16 teams played a single-elimination tournament, with the teams split into the two regions until the final. Each tie was played on a home-and-away two-legged basis. The away goals rule, extra time (away goals do not apply in extra time) and penalty shoot-out were used to decide the winner if necessary (Regulations Article 11.3).[2]
The schedule of each round was as follows.[1] Matches in the West Region were played on Mondays and Tuesdays, while matches in the East Region were played on Tuesdays and Wednesdays.
| Round | First leg | Second leg | |
|---|---|---|---|
| Round of 16 | 7–9 May 2018 | 14–16 May 2018 | |
| Quarter-finals | 27–29 August 2018 | 17–19 September 2018 | |
| Semi-finals | 2–3 October 2018 | 23–24 October 2018 | |
| Final | 3 November 2018 | 10 November 2018 |
The bracket of the knockout stage was determined as follows:
| Round | Matchups | |
|---|---|---|
| Round of 16 | (Group winners host second leg)
| |
| Quarter-finals | (Matchups and order of legs decided by draw, involving four round of 16 winners each in West Region and East Region)
| |
| Semi-finals | (Winners QF1 and QF3 host first leg, Winners QF2 and QF4 host second leg)
| |
| Final | (Winner SF2 host first leg, Winner SF1 host second leg, as reversed from previous season's final)
|
In the round of 16, the winners of one group played the runners-up of another group from the same region, with the group winners hosting the second leg, and the matchups determined by the group stage draw.
|+West Region|+East Region
4–4 on aggregate. Persepolis won on away goals.----Al-Sadd won 4–3 on aggregate.----Esteghlal won 3–2 on aggregate.----Al-Duhail won 8–3 on aggregate.
2–2 on aggregate. Tianjin Quanjian won on away goals.----Jeonbuk Hyundai Motors won 4–3 on aggregate.----Suwon Samsung Bluewings won 3–1 on aggregate.----Kashima Antlers won 4–3 on aggregate.
The draw for the quarter-finals was held on 23 May 2018.[5] In the quarter-finals, the four teams from the West Region played in two ties, and the four teams from the East Region played in two ties, with the matchups and order of legs decided by draw, without any seeding or country protection.
|+West Region|+East Region
Al-Sadd won 5–3 on aggregate.----Persepolis won 3–2 on aggregate.
Kashima Antlers won 5–0 on aggregate.----3–3 on aggregate. Suwon Samsung Bluewings won 4–2 on penalties.
In the semi-finals, the two quarter-final winners from the West Region played each other, and the two quarter-final winners from the East Region played each other, with the order of legs determined by the quarter-final draw.
|+West Region|+East Region
Persepolis won 2–1 on aggregate.
Kashima Antlers won 6–5 on aggregate.
See main article: article and 2018 AFC Champions League Final. In the final, the two semi-final winners played each other, with the order of legs (first leg hosted by team from the East Region, second leg hosted by team from the West Region) reversed from the previous season's final.Kashima Antlers won 2–0 on aggregate.