Each tie in the knockout phase, apart from the final, is played over two legs, with each team playing one leg at home. The team that scores more goals on aggregate over the two legs advances to the next round. If the aggregate score is level, the away goals rule is applied, i.e. the team that scores more goals away from home over the two legs advances. If away goals are also equal, then extra time is played. The away goals rule is again applied after extra time, i.e. if there are goals scored during extra time and the aggregate score is still level, the visiting team advances by virtue of more away goals scored. If no goals are scored during extra time, the winners are decided by a penalty shoot-out. In the final, which is played as a single match, if the score is level at the end of normal time, extra time is played, followed by a penalty shoot-out if the score is still level.
The mechanism of the draws for each round is as follows:
In the draw for the round of 16, the eight group winners are seeded, and the eight group runners-up are unseeded. The seeded teams are drawn against the unseeded teams, with the seeded teams hosting the second leg. Teams from the same group or the same association cannot be drawn against each other.
In the draws for the quarter-finals and semi-finals, there are no seedings, and teams from the same group or the same association can be drawn against each other. As the draws for the quarter-finals and semi-finals are held together before the quarter-finals are played, the identity of the quarter-final winners is not known at the time of the semi-final draw. A draw is also held to determine which semi-final winner is designated as the "home" team for the final.
For the quarter-finals and semi-finals, teams from the same city are not scheduled to play at home on the same day or on consecutive days, due to logistics and crowd control. To avoid such scheduling conflict, if the two teams are drawn to play at home for the same leg, the order of legs of the tie involving the team with the lower domestic ranking in the qualifying season is reversed from the original draw.
Qualified teams
The knockout phase involved the 16 teams which qualified as winners and runners-up of each of the eight groups in the group stage.
The draw for the round of 16 was held on 17 December 2018, 12:00 CET. Manchester United became the first team in UEFA Champions League history to advance after losing at home by two goals or more in the first leg. Including the European Cup era, only Ajax managed this feat, winning a play-off match they forced in the 1968–69 European Cup quarter-finals against Benfica after losing 1–3 in the first leg at home and winning 3–1 in the second leg away.
Summary
The first legs were played on 12, 13, 19 and 20 February, and the second legs were played on 5, 6, 12 and 13 March 2019.
Matches
Manchester City won 10–2 on aggregate. ---- Juventus won 3–2 on aggregate. ---- 3–3 on aggregate. Manchester United won on away goals. ---- Tottenham Hotspur won 4–0 on aggregate. ---- Barcelona won 5–1 on aggregate. ---- Porto won 4–3 on aggregate. ---- Ajax won 5–3 on aggregate. ---- Liverpool won 3–1 on aggregate.
Quarter-finals
The draw for the quarter-finals was held on 15 March 2019, 12:00 CET.
Summary
The first legs were played on 9 and 10 April, and the second legs were played on 16 and 17 April 2019.
Matches
Ajax won 3–2 on aggregate. ---- Liverpool won 6–1 on aggregate. ---- 4–4 on aggregate. Tottenham Hotspur won on away goals. ---- Barcelona won 4–0 on aggregate.
Semi-finals
The draw for the semi-finals was held on 15 March 2019, 12:00 CET.
Summary
The first legs were played on 30 April and 1 May, and the second legs were played on 7 and 8 May 2019.
Matches
3–3 on aggregate. Tottenham Hotspur won on away goals. ---- Liverpool won 4–3 on aggregate.
Final
The final was played on 1 June 2019 at the Metropolitano Stadium in Madrid. The "home" team was determined by an additional draw held after the quarter-final and semi-final draws.
Borussia Dortmund
Atlético Madrid
Tottenham Hotspur
Paris Saint-Germain
Porto
Ajax
Roma