"We hoped it would be like this because last game he got better and better, minute by minute, so we wanted to build on it". Marega, who had scored in six consecutive Champions League games prior to the clash at Anfield, passed up two glorious chances.
Mohamed Salah ended his eight-game goal drought as Liverpool returned to the top of the Premier League table with a 3-1 win at Southampton on Friday, but the Egyptian got his angles wrong when he failed to double the hosts' lead with just Casillas to beat moments later.
Georginio Wijnaldum dropped to the bench for the visit of the Portuguese side but could also return to play against Maurizio Sarri's men.
"The problem was a little bit in the second half, we gave one or two counter-attacks away and then we had to control it again a bit more".
This season, Liverpool lost all their away games in the group stage of the Champions League but qualified for the knockout stage because of their impressive home form.
"Obviously we know it's going to be a tough game and to score two good goals was very important but the clean sheet was the most important thing", said the Netherlands captain.
Alexander-Arnold's potential handball was the first incident under the microscope, with Liverpool escaping punishment despite the use of VAR, in stark contrast to Tottenham's Danny Rose who was penalised for handball against Manchester City in the night's other quarter-final tie.
A selection of Liverpool supporters picked out Keita for his display, as he finally begins to come into his own. Overall, a really good performance.
Any thoughts that Liverpool's quest for a first Premier League title in 29 years would derail their Champions League campaign have been dispelled by a consummate first-leg performance. We should have played more in-behind.
Only a matter of centimetres denied Liverpool a third early in the second half when another excellent Henderson cross picked out Sadio Mane to volley home, but the Senegalese was flagged offside.
"They had a lot, it was quite uncomfortable but we defended them well".
If Liverpool score in the away leg, Porto will have to net four to go through and Steve McManaman believes they'll be fully confident of doing just that.