Chelsea were put in front by Mason Mount after 30 minutes.
He beat Porto goal-keeper Agustin Marchesin with a low-line drive at the far post.
In the second half, the likes of Christian Pulisic and Olivier Giroud replaced Timo Werner and Kai Havertz respectively.
Porto too created a number of chances to equalize, however, a late strike by Ben Chilwell powered Chelsea to victory.
Mount, Ben Chilwell attain these feats
At 22 years and 87 days, Mason Mount has become the youngest-ever goal-scorer for Chelsea in a UEFA Champions League knockout match.
As per Opta, this was the first time since March 2012 (John Terry and Frank Lampard vs Napoli) that two different English players scored for Chelsea in the same UEFA Champions League match (Mount and Ben Chilwell).
Will Chelsea win the Champions League under Tuchel?
Thomas Tuchel has become the second Chelsea manager to win his first three games in the knockout stages of Champions League. The previous manager to do so was Roberto Di Matteo in 2011/12. Notably, Chelsea won the competition in that season.
A third consecutive clean sheet for Chelsea
As stated, Chelsea kept their third consecutive clean sheet in Champions League.
They haven't allowed a goal in the last 346 minutes of European competition since Krasnodar struck in the group stage (December).
"There were many moments where we suffered," admitted Tuchel.
"But we accepted it, that's the way it is at this stage. The spirit was good and it's an excellent result."