The 2018 Copa Sudamericana second stage was played from 17 July to 16 August 2018.[1] A total of 32 teams competed in the second stage to decide the 16 places in the final stages of the 2018 Copa Sudamericana.[2]
The draw for the second stage was held on 4 June 2018, 20:00 PYT (UTC−4), at the CONMEBOL Convention Centre in Luque, Paraguay.[3] [4] For the second stage, the teams were allocated to two pots according to their previous results in this season:[5]
The 32 teams were drawn into 16 ties (O1–O16) between a team from Pot 1 and a team from Pot 2, with the teams from Pot 1 hosting the second leg. Teams from the same association could be drawn into the same tie.[6]
The following were the 10 teams transferred from the Copa Libertadores (two best teams eliminated in the third stage of qualifying and eight third-placed teams in the group stage).
| Match | Best teams eliminated in third stage | Second stage draw | |
|---|---|---|---|
| G3 |  Jorge Wilstermann | bgcolor=#BBF3BB align=center rowspan=2 | Pot 1 |
| G2 |  Banfield | ||
| Group | Third-placed teams in group stage | Second stage draw | |
| A | Defensor Sporting | bgcolor=#BBF3BB align=center rowspan=8 | Pot 1 |
| B | Bolívar | ||
| C | Peñarol | ||
| D |  Santa Fe | ||
| E |  Vasco da Gama | ||
| F | Nacional | ||
| G | Millonarios | ||
| H | Junior |
The following were the 22 winners of the first stage from the Copa Sudamericana. Matches in the first stage were considered for the ranking of teams for the second stage draw.
In the second stage, each tie was played on a home-and-away two-legged basis. 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 (Regulations Article 27).[2]
The 16 winners of the second stage advanced to the round of 16 of the knockout stages.
The first legs were played on 17–19, 25–26 July, and 1–2 August, and the second legs were played on 24, 31 July, 1–2, 7–9 and 14–16 August 2018.[7] [8] |}
----Millonarios won 5–1 on aggregate and advanced to the round of 16 (Match A).
----Botafogo won 3–2 on aggregate and advanced to the round of 16 (Match B).
----Nacional won 1–0 on aggregate and advanced to the round of 16 (Match C).
----Tied 1–1 on aggregate, Colón won on penalties and advanced to the round of 16 (Match D).
----Banfield won 2–1 on aggregate and advanced to the round of 16 (Match E).
----Fluminense won 3–0 on aggregate and advanced to the round of 16 (Match F).
----Atlético Paranaense won 6–1 on aggregate and advanced to the round of 16 (Match G).
----Deportivo Cali won 6–1 on aggregate and advanced to the round of 16 (Match H).
----LDU Quito won 3–2 on aggregate and advanced to the round of 16 (Match H).
----Caracas won 6–3 on aggregate and advanced to the round of 16 (Match G).
----Tied 4–4 on aggregate, Deportivo Cuenca won on penalties and advanced to the round of 16 (Match F).
----Defensa y Justicia won 2–1 on aggregate and advanced to the round of 16 (Match E).
----Tied 1–1 on aggregate, Junior won on penalties and advanced to the round of 16 (Match D).
----San Lorenzo won 3–1 on aggregate and advanced to the round of 16 (Match C).
----Bahia won 3–1 on aggregate and advanced to the round of 16 (Match B).
----Santa Fe won 2–0 on aggregate and advanced to the round of 16 (Match A).