The Reds raced into the lead after just five minutes when the shot of Keita - who had scored his first goal for the club in Friday night's victory over Southampton - took a wicked deflection off Oliver Torres and nestled in the corner of the net, past Iker Casillas.
In an open contest with chances at either end, Liverpool completed the scoring within 25 minutes, with both Keita and Henderson crucial in the two goals.
"Then I think due to Rafa Benitez as a manager, the way he sets his team up, I think he will make it hard for Liverpool".
Liverpool's excellent performance was also exemplified by Firmino, whose best performances have tended to come in Europe so far this season.
And, while Klopp would argue that the creativity instead comes from the full-backs - evidenced by another assist for young Alexander-Arnold here - Liverpool's lack of goals from midfield is nevertheless a weakness.
Mane thought he had scored the third just after half-time but VAR upheld the assistant referee's decision to flag him offside and from that point Liverpool lost their way somewhat as Porto, who have now not won in any of their 20 visits to England, chose to make a game of it.
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"A really, really good result", Jurgen Klopp called it. There were some good moments in the game [but] obviously we can do better. It's a lovely, lovely team goal.
"We started well but the first time they get a chance, it's bad luck for us".
The Liverpool forward comes over the top of the ball and clearly plants his studs onto the shin of his opponent. There were gaps which Porto's players will feel they could and should have exploited.
"Hendo's a brilliant player and I'm really happy he can show that again", grinned Klopp in his post-match news conference. "We've not used him there for 3.5 years - sorry about that!" grinned Klopp. He obviously likes the position. Should Liverpool win their match against the Portuguese champions, they will face Ole Gunnar Solskjaer's side or the Catalans.
Porto go to mid-table Portimonense on Saturday before hosting Liverpool.
"If you ask all the other lads they'll tell you the same thing: what Mo gives us can't just be measured in the goals he scores himself". It wasn't as conclusive as a year ago, but it will be hard for Porto to overturn a 2-0 deficit in the second leg, you feel.