The sides were forced to play on neutral ground because of COVID-19 restrictions in Spain that prohibited Chelsea from making the trip to Madrid.
Olivier Giroud's overhead kick was the fixture's decisive score. The goal was the subject of a video review after the Frenchman was originally judged to be offside. Subsequently replays showed Atletico defender Mario Hermoso had the final touch, thereby nullifying the offside, before Giroud's incredible piece of individual skill:
Chelsea's form has turned around upon naming Thomas Tuchel as their new manager on Jan. 26. They drew with Wolverhampton Wanderers one day later before reeling off five straight wins. A draw with Southampton last Saturday ended the streak.
Atletico's results have been a little more patchy after they looked like the clear favorites to win La Liga. Los Rojiblancos took five points from their last four league fixtures. Real Madrid are now just three points back in second place, though Atletico have a game in hand.
That perhaps explains why Atletico Madrid manager Diego Simeone adopted a more defensive approach.
Timo Werner forced Jan Oblak to make a save at his near post in the 39th minute, which was the closest either side came to scoring in the first half.
Atletico remained rigid as the second half got underway.
The match opened up a bit more as Chelsea made better use of the possession it enjoyed. That, in turn, left the Blues a bit more exposed on the counterattack.
On the whole, Chelsea were deserved victors. They finished with 59 percent of possession and failed to allow a single shot on target from their opponents.
While Simeone seemed to be playing for the draw, a 1-0 loss isn't the end of the world because overcoming a one-goal deficit isn't an impossible task. The club toppled reigning champions Liverpool 3-2 at Anfield in the round of 16 in last year's tournament.
Chelsea will also be without Jorginho and Mason Mount for the second leg because oof yellow cards they picked up Tuesday night.
From a neutral perspective, Giroud's goal was a welcome development because it will force Atletico to abandon the defensive shell they deployed. Simeone already displayed a change in tactics when he brought on Moussa Dembele, Lucas Torreira, Renan Lodi and Vitolo within the space of three minutes deep into the second half.
Tuchel, meanwhile, will be feeling comfortable about his squad's chances of advancing to the quarterfinals—especially with a crucial away goal in a tiebreaker.
This isn't the kind of performance that will live long in the memory of supporters, but the Blues made the leaders in La Liga look pretty ineffective. Snagging an away goal and keeping a clean sheet was a great outcome.
The second leg is scheduled for March 17 at Stamford Bridge. In the meantime, Atletico are back in league action at sixth-place Villarreal on Sunday, when in a major Premier League clash, fifth-place Chelsea are home against second-place Manchester United.