Mason Mount scored the opening goal on the night with a sensational turn and low drive following an incisive pass from Jorginho. Ben Chilwell then rounded the goalkeeper to tap into an empty net with five minutes remaining to score his first goal in the competition, and give Chelsea a huge advantage at the halfway stage of the tie.
The Blues had been second best for much of the game, though, with Porto enjoying the lion's share of possession and having more chances on goal. Pepe forced Edouard Mendy into a smart save while Mateus Uribe skimmed the top of the net with a volley. In the second half, Moussa Marega saw an angled effort blocked by Mendy, while Luis Diaz threatened with a low effort that flashed just wide of the post.
Porto were compact and patient without the ball, and tough for Chelsea to break down. In attack they were dangerous from set pieces and their one-touch play around the box caused problems. In contrast, the Blues seemed rather fortuitous to keep a clean sheet, but crucially they were clinical in the final third when it mattered.
Despite the game being played in a neutral venue because of travel restrictions in light of the COVID-19 pandemic, it was a classic away performance from Chelsea. They had to endure spells of pressure, but they took their chance well to break the deadlock. The Blues are only the third team to score against Porto in the Champions League this season.
Chelsea were second to everything when it came to set pieces and crosses, which will be a concern to Thomas Tuchel.
Manager rating out of 10
7 -- Chelsea were fortunate to keep a clean sheet, but Tuchel has made them harder to beat. He identified that the Kai Havertz-Timo Werner attacking partnership wasn't working, and rightly replaced them.
Player ratings (1-10; 10 = best, players introduced after 70 minutes get no rating)
GK Edouard Mendy, 8 -- Mendy was alert to keep out an in-swinging Porto corner, and he had to make a good save to his left to deny a Pepe header. After the break, he narrowed the angle successfully to block Marega. He now has seven clean sheets in eight Champions League matches this season.
DF Cesar Azpilicueta, 5 -- The skipper made a great block to deny a certain goal-bound effort just before half-time, and had a good chance to score with a header, but overall he had a tough evening.
DF Andreas Christensen, 6 -- Returning to the side, the centre-back was continually looking for the cross-field ball to Reece James, but he tended to overhit it. Apart from that, he read the game excellently throughout.
DF Antonio Rudiger, 6 -- Like Christensen, Rudiger was also looking for the cross-field ball, but to Chilwell, and he had little success with it. Defensively, Chelsea were beaten in the air too many times, particularly at set pieces, but Rudiger did make some key interventions.
MF Reece James, 8 -- This was another impressive night for James, who not only had acres of space on the right-hand side, but he also refused to let anything get past him.
MF Jorginho, 6 --The Italy international had a disappointing match and struggled to keep Porto at bay, although he provided a key moment when his inch-perfect assist found Mount for the opening goal.
MF Mateo Kovacic, 7 -- Playing in his 50th Champions League match, he tried to exploit Porto's high line with a series of passes over the top into the channels, but it wasn't an effective strategy. The Kovacic-Jorginho pivot was second best at times.
MF Ben Chilwell, 7 -- Solid at the back and keen to get forward, Chilwell tried to stretch a compact Porto middle. He was pressed by several players throughout and always seemed to find a way out. He took his goal well, and his strike could be pivotal in the tie.
FW Mason Mount, 8 -- Opened the scoring with a superb finish. He turned sensationally with his first touch and then struck the ball across the goalkeeper and into the far corner.
FW Kai Havertz, 4 -- The Germany forward seemed unsure of his role, confused as to whether he was playing as a striker or as a No.10. He had a glorious chance to score on the hour mark, and although he was adjudged to have been offside, he missed anyway.
FW Timo Werner, 6 -- After a quiet first half in which he had few touches, he came close to doubling the advantage after the break when his header finished just over the bar. Worked tirelessly but had little to show for his efforts.
FW Christian Pulisic, 6 -- Showed good ability when he came on and retained possession in tight spaces. He then hit the crossbar moments before Chelsea added a second.
FW Olivier Giroud, 6 -- The French World Cup winner started the move alongside Kovacic that saw Pulisic hit the bar, and Chelsea looked more potent with him leading the line.
MF N'Golo Kante, N/R -- Kante brought fresh energy to the game and was everywhere at once as Chelsea's midfield looked increasingly solid. His passing was erratic at times, but his addition was a huge positive.
MF Emerson, N/R -- Came on in injury time and had little chance to get involved.