2018 Copa Sudamericana final stages
The 2018 Copa Sudamericana final stages were played from 21 August to 12 December 2018. A total of 16 teams competed in the final stages to decide the champions of the 2018 Copa Sudamericana.
Qualified teams
The 16 winners of the second stage advanced to the round of 16.Seeding
Starting from the round of 16, the teams were seeded according to the second stage draw, with each team assigned a "seed" 1–16 corresponding to the tie they win .
| Seed | Match | Second stage winners |
| 1 | O1 |  Millonarios |
| 2 | O2 |  Botafogo |
| 3 | O3 |  Nacional |
| 4 | O4 |  Colón |
| 5 | O5 | Banfield |
| 6 | O6 | Fluminense |
| 7 | O7 | Atlético Paranaense |
| 8 | O8 | Deportivo Cali |
| 9 | O9 |  LDU Quito |
| 10 | O10 |  Caracas |
| 11 | O11 | Deportivo Cuenca |
| 12 | O12 | Defensa y Justicia |
| 13 | O13 | Junior |
| 14 | O14 | San Lorenzo |
| 15 | O15 | Bahia |
| 16 | O16 | Santa Fe |
Format
Starting from the round of 16, the teams played a single-elimination tournament with the following rules:
- Each tie was played on a home-and-away two-legged basis, with the higher-seeded team hosting the second leg.
- In the round of 16, quarterfinals, and semifinals, if tied on aggregate, the away goals rule would be used. If still tied, extra time would not be played, and the penalty shoot-out would be used to determine the winner.
- In the [|finals], if tied on aggregate, the away goals rule would not be used, and 30 minutes of extra time would be played. If still tied after extra time, the penalty shoot-out would be used to determine the winner.
Bracket
| Round | Matchups |
| Round of 16 |
|
| Quarterfinals |
|
| Semifinals |
|
| Finals |
|
The bracket was decided based on the second stage draw, which was held on 4 June 2018.
Round of 16
The first legs were played on 21–22 August, 18–20 and 26 September, and the second legs were played on 19, 25, 27 September, and 2–4 October 2018.Match A
----Tied 0–0 on aggregate, Santa Fe won on penalties and advanced to the quarterfinals.
Match B
----Tied 3–3 on aggregate, Bahia won on penalties and advanced to the quarterfinals.
Match C
----Tied 3–3 on aggregate, Nacional won on away goals and advanced to the quarterfinals.
Match D
----Junior won 2–1 on aggregate and advanced to the quarterfinals.
Match E
----Defensa y Justicia won 2–0 on aggregate and advanced to the quarterfinals.
Match F
----Fluminense won 4–0 on aggregate and advanced to the quarterfinals.
Match G
----Atlético Paranaense won 4–1 on aggregate and advanced to the quarterfinals.
Match H
----Tied 1–1 on aggregate, Deportivo Cali won on penalties and advanced to the quarterfinals.
Quarterfinals
The first legs were played on 23–25 October, and the second legs were played on 30–31 October and 1 November 2018.Match S1
----Santa Fe won 3–2 on aggregate and advanced to the semifinals.
Match S2
----Tied 1–1 on aggregate, Atlético Paranaense won on penalties and advanced to the semifinals.
Match S3
----Fluminense won 2–1 on aggregate and advanced to the semifinals.
Match S4
----Tied 3–3 on aggregate, Junior won on away goals and advanced to the semifinals.
Semifinals
The first legs were played on 7–8 November, and the second legs were played on 28–29 November 2018.Match F1
----Junior won 3–0 on aggregate and advanced to the finals.
Match F2
----Atlético Paranaense won 4–0 on aggregate and advanced to the finals.
Finals
In the finals, if tied on aggregate, the away goals rule would not be used, and 30 minutes of extra time would be played. If still tied after extra time, the penalty shoot-out would be used to determine the winner.The first leg was played on 5 December, and the second leg was played on 12 December 2018.
----
Tied 2–2 on aggregate, Atlético Paranaense won on penalties.