Porto were without Sergio Oliveira, whereas Chelsea featured Kai Havertz, Timo Werner and Mason Mount from the embarrassing loss to West Bromwich Albion.
It was the Premier League side that made the early inventions on the home side's goal courtesy of smart movements from Havertz, but he didn't bring any trouble to the Portuguese heavyweights.
Chelsea did ultimately go on and break the deadlock two minutes from the half-hour mark with a first-time strike from Mount following a precision ball towards the six-yard area from Jorginho.
The Dragons could've gone level through the head of Pepe from a corner-kick, but the attempt was tipped away by goalkeeper Edouard Mendy two minutes before halftime.
Thomas Tuchel's side, who just suffered a 5-2 loss to West Brom, entered the second half gunning for a cushion strike as a header from Werner after a cross by Mount sailed clear.
Porto dusted off the slow first half and started to make more threats inside the closing stages, but Moussa Marega amongst others couldn't profit.
The Blues regained control towards the last 20 minutes and could've gone two goals up through a header from Cesar Azipilicueta from a free-kick by Reece James, but the Spaniard fluffed.
A double substitution from the Blues followed midway in the second half, with Christian Pulisic introduced for Werner and Havertz sacrificed for Olivier Giroud.
Chelsea made the result safe five minutes before time through a simple tap-in from Ben Chilwell after he ran in from the left of the area, as it finished 2-0 with the return-leg next Tuesday.