How do you break down a team that shapes up in a 6-3-1 formation out of possession?
It's a question Chelsea were forced to try and find an answer to when they travelled to Bucharest to take on Atletico Madrid on Tuesday night.
Even by Diego Simeone's obsessively high standards of defensive solidity, his team were in a particularly stingy mood in Romania. That opening gambit is not a misprint. Each time Atletico lost the ball, a flurry of Rojiblancos shirt retreated to their own 18-yard line.
Centre backs Mario Hermosa, Stefan Savic and Felipe, wing backs Thomas Lemar and Marcos Llorente, and right forward Angel Correa would respond to El Cholo's raspy screams, teaming up to create one of the most imposing low blocks in world football.
Collectively, the system would pose problems to any set of attackers. However, the remarkable talent of each of its composite parts - even with the absences of Kieran Trippier and Jose Gimenez - made Chelsea's task even harder. Each member of this seemingly impregnable defensive wall has contributed significantly to an Atleti team that has conceded just 16 goals in La Liga this season and shipped just eight in a Champions League group containing the irrepressible Bayern Munich.
Despite all of this, the Blues still managed to escape from the contest with a win and, perhaps more importantly, a crucial away goal. They had Olivier Giroud to thank for this, a player who has seemingly been on the cusp of being shipped out of Stamford Bridge for the past two years.
The once unwanted Frenchman netted one of Chelsea's great European goals. Latching onto Marcos Alonso's diverted cross, he produced an overhead kick that was almost as beautiful as his chiseled jawline.
Looking at things more widely, Thomas Tuchel can take plenty of positives from his side's performance as a whole.
Before Giroud's freakishly brilliant strike settled the game in the second half, there were plenty of signs that Chelsea were slowly piecing together the right combinations to break down their joy-sapping opponents.
Many sides have registered monstrous amounts of possession when facing Atletico in a European knockout tie, but Chelsea were part of a select few that actually managed to threaten their opponents.
Key to this were the displays of supporting forwards Timo Werner and Mason Mount. Their approaches to breaking down the home side's defence varied, but both were effective at points. Werner opted for lightning quick exchanges on the edge of the box with Giroud. This tactic paid off on several occasions as well, with the German looking the sharpest player on the pitch by some distance.
Mount, meanwhile, drifted around in the half spaces, looking to switch the play quickly with a deep cross or set free his teammates with an incisive pass. These pair of young upstarts were supported by Chelsea's wing backs whose runs helped to force overloads in wide areas. Jorginho's long, crossfield passes were important as well.
This contest was billed as a litmus test for Tuchel's new look side and the results were extremely positive. Breaking down Atletico is one of the toughest tasks any European side can be posed but the Blues rose to the challenge, showcasing invention in the final third to establish themselves as favourites to progress when the pair meet for the second leg on 17 March.