Despite all Jose Mourinho's complaints, and all the pre-game complications, the reality of today is rather simple. Chelsea must avoid defeat at Anfield to stay in the title race, and beat Liverpool to turn it on its head. To do either, they will have to manage what virtually everyone else has found impossible: disrupt the most prolific English attack since 1945.
There is, however, a twist to that. Chelsea are the last team to beat Liverpool in the League, and pretty much the only side since December to look properly superior to the table leaders in a single match. It is one reason why this match looks so potent, even if Mourinho's pre-game mood has fostered a sense of anti-climax. Today the best defence in the Premier League must dampen the best attack.
Stop Liverpool starting
Brendan Rodgers's side have scored 24 goals in the opening 20 minutes of games. Such stunning starts, fuelled by the goalscoring of Luis Suarez have not just finished matches early, but fostered so much brilliant football. As the opposition chase, they leave more space. It is remarkable how many teams fall into the trap, most notably Manchester City. Chelsea are unlikely to naively leave those kind of open trenches behind, but the wonder is which way they will try to ensure that. Last Tuesday against Atletico Madrid they set up a phalanx of seven players. Against Liverpool at Stamford Bridge, they forced Rodgers' team back. The difference could be the key to winning, rather than just avoiding being blown away.
Withstand the whirlwind
Even if Chelsea prevent the early deluge, that's only half the task. There is still the variety and vigour of Liverpool's attacking. It's almost pointless to pick out any individuals because Daniel Sturridge, Suarez and Raheem Sterling are equally devastating in different positions. It is the kind of unpredictability that is the antithesis of Chelsea's dogged defensive durability, and the ultimate challenge to it. Many of Mourinho's greatest victories have come in creating something destructive, particularly with Inter. He may need something new here. The positioning of obedient but obdurate defenders like Cesar Azpilicueta will be telling.
Expose defensive errors
It is one of the wonders of Liverpool's campaign, almost as much as the swift leap from seventh to first. They are top despite conceding 44 goals. Two more and it would be the worst by a title winner in a 38-game Premier League season, beating Manchester United in 1995. Those strikes have come through individual errors by the likes of Simon Mignolet, an inability to close gaps in defence and long shots. Chelsea must expose those flaws, to the extent they make a difference to the final score. That will require the thrust they displayed in the game at Stamford Bridge, but also a few extra risks. Mourinho must strike a perfect balance.
Plug the supply
While Suarez most completely represents Liverpool's play, Jordan Henderson represents their transformation. His running links Steven Gerrard's solid base with all that fluid movement up front. Rodgers just about survived without Henderson against Norwich. Chelsea can use that absence to link their own defence and attack, dulling Liverpool. The drive of Nemanja Matic will be crucial.
Maintain focus and test Liverpool's belief
Despite some of Mourinho's comments this week, and for all his theatrics, it's difficult not to believe he's prioritising Wednesday against Atletico Madrid. That would be jarring, because Chelsea have displayed a genuinely exceptional focus in these big League matches. It is another reason why this fixture has been so eagerly anticipated: Liverpool's relentless winning run against Chelsea's brilliant big-game record. It is also a challenge Rodgers' side haven't quite faced in this run-in. For all their wondrous football, they haven't yet been brought right to the wire in a match since Fulham in February. We know how Chelsea react in such situations. We don't know how Liverpool do. That could certainly be revealing.
Lacking some key players, Chelsea look less set to surge forward as they did against Liverpool in last December's reverse fixture at Stamford Bridge. An attritional draw seems likely.