Thomas Tuchel's men secured a crucial win against Atletico Madrid thanks to a second-half strike from Olivier Giroud.
Throughout the first half, Chelsea was in control of proceedings but failed to convert their chances.
In the second half, Olivier Giroud netted for the Blues. However, it was immediately ruled offside. After consulting with VAR, the goal was awarded.
The final exchanges saw Chelsea hold on. Tuchel's men now have that big away goal going into the second leg.
Here's our five things we learned from Chelsea's win:
1. Chelsea have that all-important away goal
In a knockout tie, it is a must that the away team gets that away goal. Going into the second leg, the onus is on the opposing side to come out and pile on the pressure. Throughout the showdown with Atletico Madrid, Chelsea were always on the front foot. The Blues may not have had many clear cut chances, but they scored when it mattered. Olivier Giroud's fine effort in the second half have given Tuchel's side a big chance going into the second leg.
2. Mason Mount missing for the second leg will be a big miss
From the kick-off, a yellow card for either Jorginho, Kovacic or Mount would see them ruled out of the second tie. Both Mount and Jorginho picked up a booking. The young Englishman was booked in the early exchanges. Mount has arguably been the Blues' best player throughout the season. Although the showdown with Atletico wasn't Mason's finest display, he will be missed. His sheer presence just adds that little bit of quality and truly benefits Chelsea in any game.
3. Defensively, the Blues are still a bit shaky
In the early exchanges, the backline and the keeper looked a bit dodgy. A lack of communication and perseverance may have given Atletico some confidence going forward. It was clear that the Blues missed the sheer leadership and quality from Thiago Silva. The Brazilian should be back for the second leg. If the Blues are to progress through, then they will need Silva fully fit and in form. It's fair to say that he has been one of the signings of the summer.
4. The midfield pairing might be an issue going forward
Both Mateo Kovacic and Jorginho deserved a little bit of the plaudits at the start of Tuchel's reign. However, with that being said, if the Blues are to get to that next level, they need a creative midfielder. Chelsea are calling for a player who can split any defence. There were several opportunities for the Blues to break down and cut through Madrid's backline but failed to create those clear chances.
5. Chelsea poor in the final third once again
In the game with Southampton, it was evident that Chelsea lacked finesse in the final third. Even in the clash with Atletico, the Blues got into some real threatening positions but really failed to make the most of those positions. Going forward, this may cost the Blues dearly if they are unable to punish teams ruthlessly. Simeone's side were set up in a strong manner, with better decision making, Chelsea could have scored another.
Next up for Thomas Tuchel's side is Manchester United in the Premier League.