Chelsea were handed arguably the toughest Champions League last 16 tie that they could have hoped for when they were drawn against Atletico Madrid.
The three-time Spanish champions - responsible for knocking Manchester City out of the competition in the last two seasons - are not quite the side they once were, but as unseeded last 16 draws go, this was as tough as they come.
Chelsea were dealt a blow before kick off with captain and centre half stalwart Magdalena Eriksson ruled out with injury, leaving versatile defensive midfielder Sophie Ingle to fill the void in the heart of the Blues backline.
However, before the game was even 20 minutes old, this slightly makeshift backline had become a fully improvised foursome as Ingle saw red for bringing down Rasheedat Ajibade. Full-back Maren Mjelde shifted to centre half and winger Niamh Charles was introduced at right back.
Down to 10 players with a hastily assembled back four and facing the prospect of conceding a number of away goals, the side tipped as capable of rivalling Lyon for Champions League glory were suddenly starring down the barrel of an early exit.
Instead, the Blues turned in a stunning team performance and will remarkably take a 2-0 lead into next Wednesday's second leg.
Ann-Katrin Berger saved Deyna Castellanos' spot kick, and Chelsea's fighting spirit kicked in.
It was such a terrific team display, it was easy to forget that Chelsea were playing with a player down. This was down to the fluidity of their system and the versatility of their players; Fran Kirby was operating as a wide forward when the Blues were in possession, but then tucked in to make a midfield four when out of possession. Pernille Harder was seemingly simultaneously operating as a number eight and number 10.
Bringing on Charles was a masterstroke from Emma Hayes. The 21-year-old is accustomed to playing as a flying winger, but when the Blues went down to 10, the Chelsea boss opted for Charles to slot in at fullback instead of natural right back Hannah Blundell.
With Charles' pace, energy and athleticism, she was as good as having an extra player on the pitch. Her natural winger instincts kicked in when Chelsea were in possession as she tore up and down the right flank, while simultaneously diligently sticking to her defensive duties.
Up top, Sam Kerr put in one hell of a shift. The Australian forward is renowned for the timing of her runs and predatory, fox in the box striker's instinct. But on Wednesday evening, she did absolutely everything; she was a one woman front three.
Kerr held the ball up, she worked the channels, she ran at the Atletico back line. The 27-year-old won the Chelsea penalty from which Mjelde opened the scoring, and teed up Kirby for Chelsea's second.
With every Chelsea player putting in such a tireless shift and the team being so smart and efficient in possession, it was impossible to see where the void left by Ingle's dismissal was.
With nine minutes remaining, Atletico were offered a way back into the tie following a clumsy Berger challenge in the box, but the Chelsea keeper redeemed herself with a second spot kick save, this time from Merel van Dongen.
Having saved a Georgia Stanway penalty during Chelsea's 3-3 draw with Manchester City in February 2020 - a result that ultimately won the Blues the WSL title - Berger again proved herself as the woman for the big occasions.
This was a rare Chelsea display where they were up against it and forced to dig in and show their resilience in the face of adversity. They passed the test with flying colours, and the rest of Europe should be absolutely terrified.