Liverpool take on Portuguese champions Porto in the second leg of their Champions League quarter-final tie, which they currently lead 2-0.
Both teams will have the benefit of the Video Assistant Referee (VAR) for their eagerly-anticipated showdown.
UEFA’s executive committee approved the use of VAR for the latter stages of the tournament last December, much to the annoyance of many.
If necessary, the referee can refer to VAR when a goal has been scored, an incident has taken place inside the penalty area, a red card has been issued or there’s been a case of mistaken identity.
Liverpool’s bitter rivals Manchester United benefited from VAR in the second leg of their last-16 tie with Paris Saint-Germain when they were awarded a stoppage-time penalty which sent them through to their first quarter-final in five years.
Also in effect tonight will be the away goals rule, which applies in the event of a tie being level after both legs.
UEFA’s rulebook says: “For matches played under the knockout system, if the two teams involved in a tie score the same number of goals over the two legs, the team which scores more away goals qualifies for the next stage.
“If this procedure does not produce a result, i.e. if both teams score the same number of goals at home and away, two 15-minute periods of extra time are played at the end of the second leg.
“If both teams score the same number of goals during extra time, away goals count double (i.e. the visiting team qualifies for the next stage).
“If no goals are scored during extra time, kicks from the penalty mark determine which team qualifies for the next stage.”
Quadruple-chasing Manchester City will also have to be aware of the rules regarding VAR and away goals in their quarter-final clash against Tottenham.
Liverpool go into tonight’s match at the Estadio Drago with a healthy lead and are favourites to reach their second consecutive Champions League semi-final.
Reds boss Jurgen Klopp isn’t taking Sergio Conceicao’s side lightly, though, saying: “In Porto, we finished them off. Tonight we didn’t.
“The game is still on, we have to go there and fight.
“Porto will try to strike back. It will be a tough game but that is what you expect in the quarter-finals of Champions League.
“There is still a lot to do, the atmosphere will be really tough and intense. This is the result we wanted before the game.”