Cesar Azpilicueta vs. Filipe Luis: Breaking Down Chelsea's Left-Back Battle

Cesar Azpilicueta has won the left-back battle with Filipe Luis at Chelsea, but has he won the war?

Judging by recent rumours surrounding Luis' Stamford Bridge future, he just might have—again.

Azpilicueta has already seen off Ashley Cole, and last month the Evening Standard's Simon Johnson was linking Luis with a move back to Atletico Madrid as part of a deal to bring Koke to the Premier League this summer.

It says so much about how highly regarded Azpilicueta has become under Jose Mourinho that Luis can be seen as a transfer makeweight.

When Luis arrived from Atletico last year, the expectation was that Azpilicueta would have to fight Branislav Ivanovic at right-back for a starting berth after a season in which Cole had become marginalised.

The right is the Spaniard's natural position, after all, yet throughout 2014/15 he has remained first-choice ahead of Luis at left-back. Luis has been patient, but his opportunities have been restricted by Azpilicueta's form.

He's arguably one of the world's best players at his position, so to not be a Chelsea regular must be a point of frustration for him.

Kirsty Wigglesworth/Associated Press

There aren't many teams in European football at which a world-class left-back would be second-choice to a player being deployed out of position.

Especially when we consider Luis stats alongside Azpilicueta's.

Luis has been far from a weak link in the Chelsea back line. Indeed, whenever he has featured, Chelsea have been better off—marginally.

Luis has experienced defeat just once as a Chelsea player, enjoying a win percentage of 73.9 per cent. With Azpilicueta, that currently sits at 71.4 per cent, while Chelsea have lost three games in all competitions on his watch.

P	W	D	L	Clean sheets	Goals against	Win %
35	25	7	3	16	31	71.4

Chelsea's goals-against record is slightly stronger with Luis in the line-up, too—0.86 goals conceded per game to Azpilicueta's 0.88—which suggests on the surface that the Brazilian offers more solidity at the back.

Given how Chelsea have looked suspect at times, it raises the question of why Luis hasn't been given a longer run in the first team, why Mourinho hasn't tweaked his setup.

The answer is Ivanovic.

Far from being at risk to Azpilicueta's presence, the Serbian continues to put pressure on his opposite number at left-back.

Last year it was Cole; now it's Luis.

Mourinho doesn't want to lose the qualities Ivanovic brings to this Chelsea team. He's physical, an aerial threat and also good for a goal at vital times.

Alastair Grant/Associated Press

Already this season, Ivanovic has scored in big matches against the likes of Liverpool and Paris Saint-Germain. Ivanovic roams forward and doubles up with Willian on the right, giving Chelsea plenty of strength in that area.

Ever the pragmatist, Mourinho needs a player to be restricted on the other flank, like Azpilicueta is.

Azpilicueta is a disciplined individual, and his weak left foot means he isn't able to surge forward as often as Ivanovic can. Mourinho wouldn't want him to, either.

It's all in the name of defensive balance, attacking teams but never to the detriment to the defensive setup.

They're often criticised for appearing to lack adventure, although Chelsea often play on the front foot against opponents.

P	W	D	L	Clean sheets	Goals against	Win %
23	17	5	1	7	20	73.9

We saw it in the 1-0 win against QPR last weekend, where the home side often had 10 men behind the ball to prevent Mourinho's men getting in behind them. Chelsea were forced to probe and find gaps, which were rarely forthcoming given the congested final third.

QPR's tactic was to intercept and attack in numbers, pressing Chelsea at every opportunity to force mistakes.

Ivanovic's being far more active in the opposition's half meant Azpilicueta was more restrained, slotting in alongside John Terry and Gary Cahill as a makeshift back three at times, something outlined in the graphic below:

Squawka

Luis isn't as defensively sound in this regard. He is a threat on the attack, and his instinct will always be to push forward and join those attacks.

It's only that Ivanovic is far better at doing it.

By restricting Luis this way, it's taking something away from his game. Mourinho doesn't require him to be pressuring opponents in Chelsea's own half, however; the manager needs Luis to restrict himself to being more defensive.

It's only when Chelsea have had to get themselves back into games that Azpilicueta has been sacrificed—think the 2-1 loss to Newcastle United when Luis replaced him after the hour mark in a bid to whip balls into the danger zone from deep.

As much as he enjoys his team scoring goals, Mourinho will celebrate a clean sheet just as much—and they're seen more often with Azpilicueta.

Tim Ireland/Associated Press

Chelsea have kept 16 clean sheets with Azpilicueta (0.45 per game), while it's considerably less with Luis, sitting at just seven (0.30 per game).

And when we look at where those clean sheets have come from, it strengthens the former's position all the more: Chelsea have shut out the likes of Arsenal, Tottenham Hotspur (twice), Liverpool and Everton when Azpilicueta has featured this season.

He may not be as dynamic going forward as his teammate, but when it comes to structure and building a defensive platform, Azpilicueta is the superior force.

That's why Mourinho can't resist turning to him.

Garry Hayes is Bleacher Report's lead Chelsea correspondent. All quotes were obtained firsthand unless otherwise noted. Follow him on Twitter @garryhayes