COMMENT: It's amazing what a goal can do to lift the mood inside a stadium, to loosen seized up limbs and transform a sluggish performance into something that, if not any more tactically coherent, has enough fight to give the illusion of togetherness inside the dressing room.

At half-time, with the score 0-0, boos rang out at Stamford Bridge after an inept display had left Maurizio Sarri waving his arms in exasperation from the dugout. By the time Gonzalo Higuain had dinked the ball over Ben Foster to make it 3-0 the mood was so light David Luiz felt comfortable enough to playfully squirt a water bottle at his manager.

But that first-half display ought not to be forgotten. It was in many ways a perfect encapsulation of Chelsea's season as a whole: a clumsy, chaotic chugging along that highlighted just how little the Chelsea players have taken Sarri-ball to heart. The Italian's footprint is not on this team. They lack urgency, verticality, or any semblance of the intricacy that defined Sarri's Napoli. And yet three second-half goals reminded us that, bizarrely enough, Chelsea could be about to finish third and win the Europa League in Sarri's first year – all after just three weeks at the beginning of the season for Sarri, who needs long summers of tactical preparation, to get his ideas across.

Nevertheless, at times the only discernible strategy appears to be to give it to Eden Hazard and see what he can conjure. If that wasn't worrying enough, the Belgian almost certainly won't be at the club next season. Filling that void will require one of two things: sacking the current head coach for someone more naturally aligned with the squad's Conte/Mourinho-inspired playing style or, more likely now Champions League football is on its way back to Stamford Bridge, a doubling down on Sarri's methods.

The latter option means significant investment in the team to implement the revolution Sarri was supposed to have started 12 months ago. Based on the performance against Watford on Sunday, that means reinforcements in defence, midfield, and attack.

Let's start at the back. Troy Deeney dominated on Sunday, winning 100% of his aerial battles against the Chelsea centre-backs to set the tempo in the first half. Jorginho's sloppiness on the ball and frequent missed tackles or interceptions was testament to the combination of strength and speed Deeney and Gerard Deulofeu brought to the game, but between the Italian, David Luiz, and Andreas ChristensenChelsea lacked guile.

It remains a mystery why Sarri doesn't simply switch Jorginho and N'Golo Kante around. Jorginho was excellent moving forward against Watford, showing the assertiveness in possession that Kante cannot match, and if swapped the latter would strengthen Chelsea's soft centre. Just as Pep Guardiola in his first season at Manchester City learnt the importance of a holding midfielder – learnt the Premier League is too chaotic to function without one – Sarri must eventually concede that the world's best defensive midfielder ought to play in defensive midfield.

But Deeney's forceful performance was more about an absence of leadership at the back, Chelsea's deficiency in this area acutely highlighted by Gary Cahill's late substitute appearance just days after he claimed the achievements of his generation at Chelsea had not been respected by the current management. Cahill doesn't have the legs any more to have featured regularly under Sarri, but his brief appearance on Sunday was a reminder of the physical and psychological properties currently missing from Chelsea's back four. A commanding centre-back is needed.

Chelsea's problems in midfield run deeper than the Kante/Jorginho conundrum. Ruben Loftus-Cheek and Matteo Kovacic are good footballers, but once again neither player could stamp their authority on the Watford game; both are missing the speed of thought and quickness of movement required for the intensity of Sarri-ball. This is probably the hardest position to fill, but what Chelsea need is a playmaker who will consistently seek the ball, who will swirl and shimmy for 90 minutes to keep the possession meaningful. In other words Chelsea need a Christian Eriksen type to replace Kovacic – a man unlikely to make his loan move permanent after underwhelming across 31 league games (no goals, two assists).

In attack, Christian Pulisic is inbound, yet Chelsea simply cannot replace Hazard, who assisted twice against Watford to take his goal contributions up to 31 from 36 in the league this season. He is a unique player and at a level Chelsea - in their current situation - simply cannot attract. Signing another winger to join Pulisic, who is unlikely to settle right away, is vital given that 31-year-old Pedro and 30-year-old Willian both have just 12 months left on their contract.

Equally important is signing a new striker – and that player must not be Gonzalo Higuain, reportedly one of Sarri's main targets. The Argentine was once again too slow, and too static, against Watford. Forget the poor touches (every player needs time to adapt to the speed of Premier League football) and forget the excellent finishes (that side of his game was never in doubt); he needs to run the channels and give Chelsea's midfielders a vertical option, and he needs to drop short for a pass then spin in behind to help enact the Sarri-ball staple of incisive counters. Higuain simply does not move enough.

Tammy Abraham may get a chance after scoring 25 Championship goals on loan at Aston Villa, although Chelsea need an established star leading the line. Or, in other words, they need to sign the player Higuain was two years ago.

As the season ends Chelsea realistically need a new centre-back, midfielder, winger, and striker if they are to even begin thinking about truly implementing Sarri's tactics and challenging Man City and Liverpool. Facing a possible transfer ban and rumours of decreasing interest from owner Roman Abramovich, Chelsea may not deliver on any of Sarri's summer wish list – and that's assuming the Italian keeps his job.

And here, again, is that essential oddity, that precariousness which defines Chelsea at the moment. During the Abramovich era they have never been more in need of a summer overhaul, yet their owner has never been less involved in the project. During the Abramovich era they have rarely looked more directionless or faced such fan unrest, yet they are on the verge of a top three finish and Europa League success just one transitional year into Sarri's tactical revolution.

Beating Watford 3-0 – an emphatic end result despite a stuttering and jade performance – was a fitting show to put on before the players' traditional end of season lap of honour. Nobody really knows what will happen next or even what, exactly, to make of the club's confusing current position. But one thing is for sure. Chelsea need fresh faces, if not fresh ideas.