We might only be four games into the new Premier League season, but that means 11% of the competition's matches have already been played.

So while it is still early days, we thought we would use the international break to look at what we've learned so far.

Has David de Gea's performance level really dipped? Have new managers Maurizio Sarri and Unai Emery had much of an impact on their teams' styles of play? And is the modern left-back the new number 10?

De Gea is nowhere near his best

Scuffed drag-backs against Leicester notwithstanding, Alisson has begun his Liverpool career in fine form and heads the Premier League in both clean sheets and save percentage.

Cap tips to Alex McCarthy at Southampton and Neil Etheridge at Cardiff, who have both made five saves from clear-cut chances.

But at the bottom is David de Gea, having saved only 50% of the shots on target he's faced this season - the lowest figure in the top flight.

It is a continuation of his World Cup form rather than a resumption of the kind of performances that saw him save an additional 13 goals in 2017-18, based on Opta's expected goals model.

The Spain international has conceded 14 of the 27 shots on target he has faced for club and country since the start of the World Cup and, in the Premier League, he has conceded 0.88 goals more than would have been expected, the third-worst rate in the division.

Expected goals against - the best performers Player Expected goals conceded Goals conceded Difference Alisson (Liverpool) 3.04 1 2.04 Martin Dubravka (Newcastle) 6.26 5 1.26 Alex McCarthy (Southampton) 5.23 4 1.23 Hugo Lloris (France) 3.04 2 1.04 Neil Etheridge (Cardiff) 5.99 5 0.99 Keeper xG based on shots on target only

Expected goals against - the worst performers Player Expected goals conceded Goals conceded Difference Asmir Begovic (Bournemouth) 3.62 5 -1.38 Michel Vorm (Tottenham) 0.92 2 -1.08 David de Gea (Man Utd) 6.12 7 -0.88 Petr Cech (Arsenal) 7.18 8 -0.82 Fabri (Fulham) 4.34 5 -0.66 Keeper xG based on shots on target only

Chelsea and Arsenal's styles are evolving fast

Unai Emery (left) won 10 trophies in spells with Sevilla and Paris St-Germain, while Maurizio Sarri has yet to win one as a manager

London's two most successful football clubs both appointed new managers in the summer. Unai Emery replaced the Premier League's third ever foreign boss at Arsenal while Maurizio Sarri became the sixth Italian to coach Chelsea.

The former was supposed to stiffen Arsenal's approach, while the latter had to take the reverse journey with a squad wound to breaking point under the intense Antonio Conte.

The two played out a curious match in week three, both sides defending appallingly at points as Chelsea won 3-2, but how are they doing overall and are they altering their teams' styles?

Chelsea are the only Premier League team to have had 100 sequences of 10 passes or more so far. That's an average of 25 per game, not far off double their average of 14 per game under Conte.

They have also completed more passes than any other side, with their average of 669 per match 197 more than last season.

If that shows a major change to Chelsea's style, it is also interesting that that figure of 25 10+ pass sequences per game is more than twice as many as an Arsenal side previously renowned for their passing style but who have looked disjointed at numerous points.

Sequences can also be used to examine the types of chances teams are creating, be they build-up attacks or direct attacks.

Build-up attacks - An open-play sequence that contains 10+ passes and either ends in a shot or has at least one touch in the box.

Direct attacks - An open-play sequence that starts just inside the team's half and has at least 50% of movement towards the opposition's goal.

Arsenal have had only two fewer build-up attacks than Chelsea, despite having far fewer 10-pass sequences. This means that when they do manage to get on the ball, they are generally making progress and getting into dangerous areas. It suggests Emery is starting to unearth the club's once-feared cutting edge.

For those who still rely on goals as their only metric of choice, it should be noted that despite having only half as many points as Chelsea, Arsenal have scored only two goals fewer. Clearly there is continued philosophical work to be done at both clubs, but they may not be as far apart as some may think.

Team Sequences of 10+ passes Build-up attacks Direct attacks Chelsea 100 17 6 Man City 90 30 9 Liverpool 82 17 12 Fulham 63 11 12 Tottenham 53 13 4 Man Utd 44 7 7 Arsenal 43 15 4 Leicester 38 6 5 Wolves 38 6 5 Everton 33 4 4

Watford are safe - and their success is built on solid foundations

Three teams boasting 100% records after four games is not common (occurring most recently in 2009 and 1969), yet Liverpool and Chelsea doing so in 2018 doesn't seem wildly unrealistic.

But not even the most fevered Watford fan would have imagined their side keeping pace into mid-September.

The Hornets are the first team from a town (as opposed to a city) to start an English top-flight season with four wins since Ipswich in 1974-75 and no side has ever been relegated after a start like this. So the Hornets are safe… but how?

Javi Gracia's team have developed a fearsome defence, currently boasting the lowest expected goals against figure and rating fifth for passes per defensive action (the average number of passes a team allows their opponents in the defensive and middle third before making a defensive intervention).

What does this mean though? It tells us that Watford are working extremely hard to disrupt their opponents and even when they are breached, the chances created against them are not great.

Team Expected goals against in 2018-19 Team Passes per defensive action per 90 mins Watford 2.56 Tottenham 8.8 Liverpool 2.72 Liverpool 9.4 Man City 2.78 Man City 9.5 Wolves 3.67 Everton 10.8 Chelsea 3.79 Watford 11.3

It seems fanciful to think that Watford can carry on like this - they started well last season under Marco Silva before fading - but this is an early season built on solid foundations.

Left-backs are key attacking weapons

Between them, Benjamin Mendy, Jose Holebas, Andy Robertson and Marcos Alonso have 12 Premier League assists already. Luke Shaw has played himself into favour with Jose Mourinho as well as scoring his first ever goal as a senior professional and setting up Marcus Rashford's goal in England's Nations League game against Spain on Saturday.

We are, it seems, into the glorious age of the creative left-back.

Mendy has produced more open-play crosses than any other player (27, followed by fellow full-backs Trent Alexander-Arnold, Kieran Trippier and Cesar Azpilicueta), while new Scotland captain Robertson has created as many chances this season as Mesut Ozil and Paul Pogba combined.

Last season 21% of the assists in the Premier League came from defenders, a proportion that has climbed to 37% in 2018-19.

Five-time Tour de France winner Bernard Hinault once said "as long as I breathe, I attack", and this is clearly now the official motto of left-backs up and down the country.