Frank Lampard's attacking philosophy has left the football world enchanted with his Chelsea side. However, he is still desperately trying to sort out his defence.
The Blues were involved in yet another thrilling encounter on Wednesday night, this time at Mestalla, but once again they were carved open at will by a Valencia team who let them off the hook with a host of unbelievable missed chances.
Chelsea can thank the abysmal finishing of Maxi Gomez and Rodrigo for the fact that Champions League qualification remains in their hands going into the matchday-six meeting with Lille at Stamford Bridge.
Lampard's line-up in Spain featured few surprises up front or in midfield but there were significant alternations at the back.
Reece James and Andreas Christensen were recalled, while Cesar Azpilicueta and Kurt Zouma featured in different positions to the ones they had played in during Saturday's Premier League loss at Manchester City.
So, in essence, this was a completely different backline to the one that took to the field at the Etihad. And it showed, with Zouma and Christensen leaving huge gaps in between them throughout the game.
The fact that the Dane hadn't played for Chelsea for two months certainly contributed to the lack of cohesion but the backline was in a general state of disarray.
Emerson had struggled at left-back against City but Azpilicueta fared little better at Mestalla and, while fellow full-back James proved a fantastic outlet going forward on the opposite flank, the youngster was repeatedly seen struggling to get back into position.
With Chelsea attacking at will but toiling defensively, the game really was as open and chaotic as the 4-4 draw with Ajax on matchday four, as Lampard acknowledged afterwards.
"It was end to end, not that we wanted that," he confessed.
The Blues boss obviously has to take the majority of the blame for his side's vulnerability at the back, with the players still struggling to various degrees with his instructions.
The net result is that he doesn't yet know his best defence.
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Fikayo Tomori has been one of the success stories of Chelsea's season so far. He was Player of the Year under Lampard at Derby County last season but few predicted he would make such a positive impact upon his return to Stamford Bridge this season.
Tomori has proven himself a centre-half of enormous promise. He has immense speed and impressive ability on the ball.
He is still only 21, though, and at times this season has been guilty of lapses in concentration, which is precisely why he wasn't selected for what was a huge game in Valencia.
Perhaps Tomori would have been trusted had Antonio Rudiger been available. Every centre-half Chelsea have would benefit from playing alongside the experienced German.
The problem is, though, that Rudiger has played only 45 minutes this season, against Wolves, after suffering a groin problem while he was recovering from the knee injury he sustained last season.
He is being sorely missed, not least because Zouma has been unconvincing, while Christensen's once seemingly inevitable rise to the top of the game has stalled.
Worryingly, Chelsea don't just have problems in the centre of defence; there are also issues at full-back, which is precisely why there is such intense interest in signing Leicester City's Ben Chilwell in January.
There is little chance of that happening, though. Even if the Court Arbitration for Sport (CAS) overturns the club's transfer ban, it would be nigh on impossible to persuade Leicester to part company with a player who has played a pivotal role in their emergence as surprise title challengers.
Consequently, Lampard will have to continue to choose between Emerson and Marcos Alonso.
The former has obvious physical and technical attributes but doubts remain over his defensive capabilities. The same could be said of Alonso, who was hauled off at half-time in the 4-4 draw with Ajax because of an error-strewn display.
The Spaniard is still struggling with the reversion to a back four, given Antonio Conte's 3-4-3 formation afforded him extra cover in defence and greater freedom to do what he does best: attack.
Azpilicueta is almost the complete opposite to his compatriot. Defending is his forte and, although he struggled at the start of the season, he has recovered strongly in recent weeks to quell talk of him being finished at the highest level.
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He remains a solid and versatile defender but is certainly lacking in the final third. He is trying to find a balance, just like Lampard.
The former midfielder has used a back three at times this season, including in the second half against Valencia, when he tried to shut up shop.
In recent weeks, he has also been asking one of his full-backs to go beyond the midfield to create an overload in an asymmetric formation.
At Mestalla, it was James, but against Man City, it was Emerson. That means that Azpilicueta is usually the man to stay back as Chelsea switch between a back four and three during the match. The change has not always been seamless.
Further issues come with Lampard's desire to give his midfielders a sense of freedom.
Previously, defensive players such as Jorginho, N'Golo Kante and Mateo Kovacic were told to sit tight. Now, they are being encouraged to get ahead of the ball and into the area, making Chelsea more dangerous in attack.
The flip side, though, is that when the ball is lost high up the pitch, the Blues are very vulnerable to counterattacks, so much so in fact, that Pep Guardiola's possession-obsessed City side were actually willing to invite Chelsea on to them at the Etihad in order to hit them on the break.
The net result is that Chelsea are scoring freely but also conceding regularly.
Lampard's side are ahead of schedule in this season of transition but it remains to be seen if the Chelsea manager can achieve a perfect balance between defence and attack.
It certainly won't be easy but, as we've seen already this season, it will be a lot of fun watching him try.