Keita put the Reds ahead in the first five minutes after his shot from outside the box was deflected by Oliver Torres and into the back of the net.
Jurgen Klopp's side doubled their advantage mid-way through the first-half as Firmino converted from Trent Alexander-Arnold's low ball across the face of the goal.
There were two moments of controversy during the game as Alisson redirected a cross on to Alexander-Arnold's hand inside the box and later Mohamed Salah followed through with his challenge on Danilo.
Both incidents were cleared by the referee and VAR, however Porto goalkeeper Casillas was keen to highlight them once again as he posted still images of both on social media.
Soy 100 por 100 optimista!! Teniendo en cuenta los resultados de octavos de @ChampionsLeague no podemos pensar que la eliminatoria está perdida. Falta el juego en Dragao y vamos a luchar por pasar a las semifinales. Gracias a todos los portistas por el apoyo en Liverpool!! pic.twitter.com/3w1xst6ULP
Speaking after the game, Casillas insisted that his side are not yet out of the tie despite not showing enough in their performance at Anfield.
"I am optimistic, we can not think that the tie is lost, we are going to fight, to try to get to the next round,” he told Movistar after the game.
“We have seven days to prepare it. We will also have to think about our championship because we also fight for the league but we will try to do better in the return leg.
"We have to be brave and move the ball, that's how we can hurt them, with speed. We are able to cover counter-attacks and we are strong on set pieces.
“Our idea is to play the way we did against Roma (in the last round), and to take advantage of our chances.
“We had a clear one tonight and if we had scored it we would have had another sensation.
"We started well but the first time they get a chance, it's bad luck for us. It hits Oliver (Torres) and I got distracted.
“They caught us cold and we tried to contain them, but they executed their plan well. They had the result in the bag when they scored the second and then we tried to adapt to the situation.
”We had our own chances and a 2-1 would have been a fairer result. The result is not very good for us, we're 2-0 down and without an away goal.
“But I'm not angry because I know the quality of our team and that we can react well if we have more of the ball and create more chances.”