8th February 2017. By Ryan Baldi.
When Chelsea forked out £30 million to re-sign David Luiz from Paris Saint-Germain on transfer deadline day in August last year, many observers wrote the move off as the ultimate panic buy.

But with Chelsea top of the league and the Brazilian defender thriving at the heart of manager Antonio Conte's back three, few still hold that view. The wild-haired defender, once a figure of ridicule, is now being hailed as one of the very best centre-backs in the Premier League.

And Luiz's transformation from a defensive liability into a crucial cog for the runaway title race leaders is all thanks to Conte's tactical mastery.

At the beginning of the campaign the Chelsea boss was intent on setting up his side in a 4-2-4 shape similar to that which he employed at Siena and during his early days in charge of Juventus.

But deteriorating results soon proved that that particular system was ill-suited to the personnel at Conte's disposal, and back-to-back defeats to Liverpool and Arsenal in September forced a rethink.

A long-time proponent of three-defender systems during his reigns at Juventus and with the Italian national team, it was speculated upon his arrival in the Premier League that Conte would implement a similar set-up at Stamford Bridge.

Many thought that the Blues would be lining up in the kind of 3-5-2 that saw the Italian tactician win three successive Serie A titles with the Bianconeri, but Conte instead elected to utilise a 3-4-3 formation like the one he favoured with the Azzurri when making his tactical switch in October.

The change brought about an immediate improvement, with Chelsea surging to the top of the table; they have only lost one league game since the 3-0 reverse against the Gunners on 24th September.

One of the main advantages of the back three is that, with the two outside central defenders the stoppers -- tasked with marking the opposition's forwards, the man in the middle of the backline benefits from fewer defensive duties and more space to get on the ball.

This role, traditionally referred to as a sweeper or libero, is perfectly suited to a defender who is comfortable on the ball, able to move forward into the midfield zone and instigate attacks with sharp forward passes. It's a role Luiz has always been perfectly suited to, but, until now, had never been given the chance to play in.

With Gary Cahill and Cesar Azpilicueta picking up the bulk of the defensive burden either side of him, Luiz's previously exposed defensive positional sense becomes far less of an issue. Instead, Chelsea benefit from being able to afford the gifted passer more time in possession and more freedom to carry the ball out from the back.

The 29-year-old former Benfica star has been a revelation since Conte's tactical adjustment, and is one of the key reasons why Chelsea's 3-4-3 has been so effective.

Fielding only two central midfielders, usually Nemanja Matic and the indefatigable N'Golo Kante, there is the potential for Chelsea to be over-run in central zones by teams who set up with three midfielders in close proximity, i.e. in a 4-3-3 or 4-2-3-1.

But with wing-backs Marcos Alonso and Victor Moses pushing high and wide at every opportunity, and with wingers Eden Hazard and Pedro supporting Diego Costa in a way more akin to inside forwards, Chelsea play the ball directly into wide attacking zones at the earliest opportunity.

This bypasses the need to build play through the centre of midfield, allowing Kante and Matic to focus their efforts on ensuring the ball stays in the high, wide areas by nipping in the bud any attempt the opposition makes to break out.

And it is Luiz, with his superb passing range, who gets himself on the ball and sprays passes out to Moses, Alonso, Hazard and Pedro to begin this process.

He is also able to step forward and augment the midfield if Kante and Matic ever need support although the former Leicester City dynamo is rarely out-gunned when it comes to midfield battles.

The switch to a back three has not only accentuated the strengths of Luiz his passing and confidence on the ball but it has also helped mask his deficiencies.

In his initial spell with the Blues, the Brazilian was regarded as gifted but error prone; a defensive risk not worth taking for managers; someone whose positional instincts and anticipation were often found wanting.

But now, in his role as the spare man at the back, his defensive duties have been simplified. He is able to sit back and sweep up behind Cahill and Azpilicueta who contest the majority of the one-on-one duels.

This has led to Luiz winning fewer interceptions (1.8) and tackles (1.2) per game than at any point during his initial stay at Stamford Bridge, but more clearances (5.4) per outing.

The stunning 30-yard free-kick he scored against Liverpool in last month's 1-1 draw at Anfield was nothing short of spectacular. But goals like that will come as no surprise to Chelsea fans who witnessed Luiz's performances for their club the first time around.

The difference now, however, is that such moments of magic are no longer interspersed with calamitous defensive errors as they once were. The stunning long-range strikes, the pin-point 40-yard passes and the breath-taking dribbles through crowded corridors are no longer sullied by wince-inducing moments of brainlessness.

Rather than being an entertaining yet flawed player whose next mistake never feels too far away, Luiz is now a defender Chelsea and Conte can believe in, a player they can trust both with and without the ball.

He will never be the kind of brick wall, take-no-prisoners defender in the mould of long-time Blues captain John Terry, but Luiz is the perfect libero at the heart of Chelsea's back three.

In an age where centre-backs were fearless, uncompromising and commanding, yet perhaps not the most technically gifted players on the pitch, Luiz would have been a lost cause.

But the modern game demands so much more of its defenders; they must now be fast, athletic and able to dictate play from deep. In that sense, Luiz was ahead of his time.

With the right guidance and allowances, the 55-cap Selecao star is everything a modern centre-back needs to be and more.

Thanks to Conte's tactical recalibration, Luiz is leading Chelsea to the Premier League title, and proving more than a few doubters wrong along the way.