Willian started the season slowly but since December has emerged as one of Jose Mourinho's most consistent and trusted performers.
Against Manchester City he did not disappoint and worked tirelessly until substituted late on.
The Brazilian winger was, for the most part, positioned as the second forward during the crucial encounter, or as Chelsea's furthest forward midfield player at least.
Defensively speaking, though, his contribution was not quite so impressive as has been the case in recent games, a vital trait for any footballer playing under Mourinho - as Mata can attest.
Willian made just one successful challenge, one header and cleared Chelsea's lines on only one occasion. However, what he did do was work hard for his side, as demonstrated by the fact he was Chelsea's most frequent passer on the night, having picked out a team-mate on 29 occasions.
Willian spent the most amount of time around the centre-circle, as opposed to having operated in the No.10 role behind the striker. He did, however, work to get into these areas when Chelsea got on the ball and also made himself available out wide on the right flank at moments when Chelsea switched to more of a 4-3-3, with Ramires slotting in alongside Nemanja Matic and David Luiz, while Willian looked to work hard down the right flank.
In terms of creating chances and motivating counter-attacks, the ex-Shakhtar man was pivotal. Whilst he failed to dribble past any opposing player, he was able to create seven chances for his team-mates and initiated a lot of key counter-attacks through breaking out of his own half.
At 0-0, during a Chelsea counter, Willian almost helped his team take the lead as he coolly slotted the ball across to Ramires, who did not manage find the back of the net but forced Joe Hart into making an important save.
Willian didn't do anything particularly spectacular throughout the 90 minutes. He didn't beat his man repeatedly like Eden Hazard did, nor did he score the brilliant winning goal like Branislav Ivanovic.
However, Willian's contribution was mainly notable in terms of the hard-work exhibited, pressing the opposition and tracking back relentlessly whenever Chelsea lost the ball. Ultimately, his pace and energy were essential in allowing Chelsea to hurry City and keep the previously rampant title-challengers contained.