A stunning bicycle kick from Olivier Giroud settled the game, with Atletico not even registering a shot on target all match.
Atletico's 'home' leg was played in the Romanian capital because the Spanish government has banned nations with mutant strains of the Coronavirus from entering the country.
The two sides are due to play the return leg at Stamford Bridge in March, but that game could still yet be moved to a neutral venue too.
So who were the standout performers?
✔️ Olivier Giroud: 7.2
Has there been a more underrated striker in English football in the last five years than Olivier Giroud.
Once again the veteran Frenchman showed his class to silence the doubters who say he is incompatible with Tuchel's football.
The 34-year-old provided Chelsea with a crucial 'away' goal with a stunning bicycle kick to decide the game.
❌ Joao Felix: 5.8
Joao Felix is having a real tough time right now and has only scored one goal since the start of December - while also contracting Covid-19.
A €126 million signing for Atletico in 2019, Joao Felix has yet to live up that price tag - the fourth highest transfer fee in history.
⭐ Cesar Azpilicueta: 8.5
The Spaniard put on a defensive clinic as Chelsea didn't miss the experienced Thiago Silva at all.
Azpilicueta won all of his six aerials, nine of his 11 duels and both of his tackles in an incredible performance at the back.
Just like when Antonio Conte was manager, Azpilicueta seems to relish playing in a back-three as Chelsea's brilliant defensive record under new coach Tuchel continues.
Chelsea have now conceded only two goals in eight games since Tuchel arrived.