It wasn't the brilliant volley just after the break that underlined Juan Mata's importance to Chelsea. It wasn't the late, curling free-kick that forced David De Gea into a full-length save either, or even the delivery from wide for the third Chelsea goal.

It was a 20-yard sideways pass to José Bosingwa in the 65th minute, with the score at 3-1, that slowed down a Chelsea attack. It annoyed Florent Malouda, who wanted a pass in front of him to attack Manchester United's new right-back Antonio Valencia, and it prompted an audible moan around Stamford Bridge.

But the pass demonstrated Mata's intelligence and awareness of the situation. Chelsea had gone 3-0 up without playing particularly good football, but had then allowed United back into the game. The second half was frantic, fast-paced and end-to-end. Chelsea, the side with the two-goal advantage, didn't want that – they needed to calm things down, kill the game, control the tempo.

Mata was the only one who understood that. His pass was unspectacular, underwhelming and lacking in ambition. But it was the right thing to do; it prompted a whole minute of pure Chelsea possession, something they struggled to recreate later on, at a time when United attack followed United attack and Chelsea made clearances when they could have played passes.

And what followed that minute of possession? A shot from Mata, controlled, precise and forcing De Gea into a smart stop down to his right. It was the perfect way to attack at that moment, to control the game, frustrate United, then pounce quickly.

Mata is the one thinker in a Chelsea side being turned into an exciting team, but one based around pace and technique rather than thoughtfulness. Villas-Boas desires a "vertical" game, but yesterday they needed to be more horizontal. Raul Meireles and Michael Essien are both box-to-box players more than holders. Daniel Sturridge and Malouda moved high up and wanted to break quickly, while Fernando Torres was naturally hunting for the goal that seems destined never to arrive. Chelsea were playing too directly and they needed someone to soothe a side full of shuttlers and scurriers.

The most intelligent footballers adjust their game and make the correct decisions according to the situation. The former Real Madrid midfielder Fernando Redondo was a master of that, described by Fabio Capello as a "tactically perfect" player, able to defend and attack equally well by using the same strengths in different ways.

Being adaptable in this respect is the final part of José Mourinho's coaching regime. He devises drills based around "guided discovery", helping the players to arrive at their own conclusions. The ultimate aim is to make his players intelligent enough to adjust the shape and style of the side according to the tactical situation in the game, without the need for input from Mourinho. He likes an on-field leader, a central midfielder who carries out the instructions and sets the tone for the rest of the side. Esteban Cambiasso did that conspicuously at Inter, while Xabi Alonso was earmarked for the role at Real Madrid.

Villas-Boas is a disciple of Mourinho, of course, and his technical leader is unquestionably Mata. The Chelsea coach spends much of his time on the touchline dictating instructions to players. He is remarkably pedantic with regard to positioning, often whistling to a defender from his odd crouching position, then gesturing for them to move a couple of yards deeper, or a couple of yards narrower.

Mata is slightly different. Villas-Boas rarely shouts to him, but often calls him over for a much longer chat, as if discussing a full-blown change in manifesto rather than a modification in policy. Mata may never be the right kind of player to be Villas-Boas's captain – and this week of all weeks, you won't get many people at Chelsea wanting to discuss the subject of captaincy – but he is unquestionably the face of Villas-Boas's Chelsea. In fact, he is the face of Villas-Boas: the two look remarkably similar when discussing the game on the touchline, and the coach towering over the playmaker while lecturing him resembles a kid taking advice from his older brother midway through a school football trial.

Villas-Boas has had to change his strategy since he came to Chelsea, in two particular ways. The first was a move from a constant "high block" to a medium or low block – in other words, moving from heavy pressing towards more of a reserved position, and in some games (most notably the crucial win over Mata's former club Valencia) dangerously close to parking the bus. The second was restricting the attacking license of the holding midfielder, for Villas-Boas ideally likes a rotating midfield triangle, demonstrated by the movement and understanding his Porto side enjoyed in midfield. "We decided it doesn't work here, so that's one of the things I have adapted," he said. "You lose a little bit of balance in the Premier League if you play that way. Transitions here are much more direct, making the importance of the number six [the holder] to stay in position more decisive."

Both moves have been more cautious, more pragmatic than his initial philosophy dictated. The next change might be to become less vertical and more patient with the ball. In home games against big sides Chelsea have twice lost points late on, to Arsenal (5-3) and Liverpool (2-1). Now they've surrendered a three-goal lead to Manchester United. Villas-Boas will explain that by stressing his commitment to attack, but it's not just a question of how much the side attacks, it's a question of how they attack.

In fairness, Chelsea did snatch the points late on against Manchester City in another big home game. But that win was secured when City went down to 10 men, Roberto Mancini moved to a very narrow 4-3-1-1 system that allowed Chelsea space down the flanks, and the home side won the decisive penalty after an attack that crossed the pitch three times, flank to flank. Sideways can be equally effective as forwards.

It was a sideways move that Chelsea needed yesterday, but a sideways move of a different kind to the one made by Villas-Boas that ultimately cost them. His decision to move Mata out to the right meant his conductor had been pushed to the margins, and Chelsea were suddenly clueless with the ball. Oriel Romeu came on, played much deeper, and Chelsea conceded the midfield ground for the final 20 minutes.

Villas-Boas is largely trying to recreate his Porto side at Chelsea, though the biggest caveat is Mata, who is unlike anyone Villas-Boas coached in Portugal. It has been assumed that Mata would learn about the Premier League in a wide role before being gradually brought into the centre, but his adaptation to the league has been remarkably swift, and Sunday's showing might be the catalyst for the decision to play him centrally permanently.

Arteta's passes earn Arsenal points

On the subject of Spanish midfielders who control the game, Mikel Arteta's importance to Arsenal shouldn't be overlooked. The departure of Samir Nasri and Cesc Fábregas means Arsenal attack less frequently through the centre and more often down the flanks, with Theo Walcott, Gervinho and increasingly Alex Oxlade-Chamberlain the key attacking components.

Arteta's job from deep is simple: to spread the play from flank to flank with calm passes. He completes around 79 passes per game, more than any other player in the Premier League, and his presence in the side certainly makes Arsenal more efficient. In the 19 games he's started this season, Arsenal have picked up 68% of points on offer – in the five he's missed, they've gained just 7% of the maximum.

Did the cold cause so many casualties?

An unusual feature of the Premier League weekend was that three sides had to make multiple substitutions before half-time. Norwich manager Paul Lambert had to replace his centre-backs Zak Whitbread and Daniel Ayala through injury, Newcastle saw both Leon Best and Ryan Taylor depart, while Stoke's Cameron Jerome and Andy Wilkinson went off, and then Robert Huth's red card forced Tony Pulis to substitute Jermaine Pennant and send on an extra centre-back.

These three incidents may have been a complete coincidence, and Taylor's was an injury due to a high tackle rather than poor conditioning, but the coldest weekend of the Premier League season coming after a rare full midweek round of fixtures probably didn't help players' muscles.