Chelsea's chances of going through to the semi-finals of the Champions League currently hang by a thread, as they fell to a 3-1 defeat to a Karim Benzema-inspired Real Madrid at Stamford Bridge six days ago.
They head into the second leg, at the newly refurbished Santiago Bernabeu, knowing that they have to do what few have achieved and come back from a 2 goal deficit to stand any chance of going through.
The Blues, however, are in the minority. Just last year, on their way to lifting the trophy, they beat the Spanish giants 2-0, albeit at Stamford Bridge. They can certainly take heart from that, but they cannot play the same way that they did 12 months ago.
101 takes a look at three key things that the London club must do to stand any chance of going through in Spain.
1. Deploy Reece James further back
The biggest problem for Chelsea in the first leg came from Vinicius Junior. Although Benzema grabbed the goals and the headlines, the Brazilian terrorised the right hand side of Chelsea's defence, forcing Andreas Christensen to be substituted at half-time.
Of course, this will nullify some of the Blues' attacking threat, with James one of the side's key creators, but they will have to find that elsewhere. Should they fall further behind, a slim chance of success will become zero.
2. Play Jorginho, N'Golo Kante AND Mateo Kovacic
N'Golo Kante was man of the match in both legs 12 months ago, but had a torrid time at Stamford Bridge in the first leg, taken off for Mateo Kovacic in the second half.
The Croatian bought more poise to the midfield, and allowed Chelsea to control the ball better, which will be key should they want to keep their opponents under pressure for long stretches of the tie by keeping possession.
Kovacic had 62 touches and made 55 passes in the second half of the first leg, compared to the measly 21 and 18 that Kante managed in the first 45 minutes, demonstrating the change that his introduction to the side brought about.
However, they still need Kante to do the dirty work for the side, with neither Kovacic nor Jorginho the most athletic midfielders and both vulnerable to being caught out by a Los Blancos counterattack.
Playing the trio together would have another bonus too, as it would allow Tuchel's side to match up with their opposition, who are almost certain to deploy Casemiro, Toni Kroos and Luca Modric across their midfield. It will be a key battleground, and one that Chelsea have to win.
3. Resist the urge to opt for pace
Against Southampton, Timo Werner made a strong case for his inclusion in future sides, bagging two goals and hitting both the post and the crossbar as Chelsea ran riot.
But, it is a case that Tuchel must ignore for this clash. While Southampton played with a high line, sitting on a 2 goal lead it is far more likely that Real Madrid drop deeper and look to counter-attack using the pace and guile of Vinicius Junior and Karim Benzema.
In this scenario, it is patience and brains that the Blues will need, not runners in behind. Mason Mount will surely occupy one of the forward berths, and with Romelu Lukaku out injured it seems likely that Kai Havertz will be deployed as a central striker.
With these tools, Chelsea could break down a Real Madrid defence that is athletic but prone to switching off at times, and should they be able to grab the early momentum of the game, they could produce a stunning comeback.
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