Liverpool had come out on top in a five-goal thriller in its Group B opener against Milan at Anfield, yet there were no such nerves on Wednesday (AEST) against an opponent it has made a habit of beating through the years.
Jurgen Klopp was in charge for 5-0 and 4-1 wins on Portuguese soil when steering Liverpool to successive final appearances in the competition in 2018 and 2019, and this year's squad appear on course to make the knockout stages once more.
Mohamed Salah and Roberto Firmino scored twice, the latter after coming on as a substitute, while Sadio Mane was also on target, making it five goals for him in as many appearances against Porto.
The result should not come as too much of a surprise, considering Porto had not managed a win in the previous eight meetings. The hosts were dealt a blow when Pepe was ruled out with an injury suffered in the warm-up, while Otavio's outing was cut short after 14 minutes.
Not long after the enforced change, Liverpool went ahead. Curtis Jones' low shot was parried by Diogo Costa onto team-mate Zaidu Sanusi, leaving Salah with a simple close-range finish.
The Porto goalkeeper did do better to deny Jordan Henderson a goal to mark his 400th appearance for the club, turning the visiting captain's fierce free-kick away, but his failure to cut out James Milner's low cross allowed Mane to tap home before the interval.
Salah slotted away his second of the game on the hour before heading to the bench and while Mehdi Taremi headed in to pull a goal back, it only served to anger Liverpool into a response.
Costa rounded out a shocking performance by straying from his area to try to reach Jones' throughball, allowing Firmino to roll the ball into an unguarded net. The Brazilian added another just four minutes later when reacting quickly to a deflection, though only after a VAR check for offside.