There's a song Chelsea fans sing about Willian.
"The s*** from Spurs bought his flight, but Willian, he saw the light,
"He got the call from Abramovich and off he went to Stamford Bridge."
For reasons of decency, we'll leave it there, but you get the gist of what the song and its subject matter is about.
There aren't many players who can sign for a club and immediately endear themselves to fans as Willian did last summer. The reason being, of course, that at the 11th hour, he opted to join Chelsea having earlier passed his medical at rivals Tottenham Hotspur, with a deal all but done.
Football had little to do with starting this love affair.
His early form for the Blues, however, made it seem Spurs had been inadvertently saved from signing an epic flop. The performances that had made Willian such a star at Shakhtar Donetsk prior to joining Anzhi Makhachkala were nowhere to be seen.
That was then. Five months on and Chelsea fans are beginning to see a return on the £30 million their club invested in the Brazilian. They're even singing his song with more regularity.
Tinkering with his starting XI, endeavoring to find his preferred line-up, Jose Mourinho now seems to have decided who will fill the key positions at Stamford Bridge. He's found his spine.
At the back, John Terry and Gary Cahill have formed a strong defensive partnership, and further forward, Eden Hazard, Oscar and Willian have put a new spin on what we knew as the Three Amigos last season.
It wasn't supposed to be that way, though. Juan Mata was spending a lot of time on the bench at the beginning of the season, and when Mourinho started giving him opportunities, it was only going to be a matter of time—excuse the pun—before he was back playing regularly.
Willian had other thoughts, clearly. Going about his work quietly, maintaining a low profile, the 25-year-old has suddenly become essential to this Chelsea team.
Whether it be his defensive duties, helping the team's attacking midfielders press their high line or breaking quick on the counter, Willian is now looking the part. Not quite a £30 million player just yet but a valuable asset nonetheless.
With Hazard and Oscar providing their undoubted flair, the partnership between the trio is now the foundation for which Chelsea have built their title challenge—one that leaves them sitting just two points behind Premier League leaders Arsenal.
For romantics and the sentimental among Chelsea fans, it has all come at a cost. There is no longer room for Mata, it seems. The Spaniard is being edged out by Willian, forced to watch on as the new recruit takes the place that was once rightfully his.
Mourinho can hardly be criticized for this development. In fact, it's praise that must follow.
Has Willian done enough to be selected ahead of Juan Mata at Chelsea?
After having his judgement questioned, it's becoming clear that the manager's vision is the right one, although for Mata, it's one that highlights how his qualities do not quite fit.
The Spaniard needs to develop his game, adjusting his attributes to suit this new-look Chelsea. It's either that or face the exit door, as Willian is showing Mata that, for all his talents, they may not be enough to succeed under Mourinho.
"The players must understand I do not work for them. I work for the club," explained the Chelsea boss in a recent interview with BBC Sport's Football Focus.
It's a philosophy that Willian has bought into—a team ethic working much to his benefit.
Where that leaves Mata, only time will tell. But the signs seem to all point one way.
Garry Hayes is Bleacher Report's lead Chelsea correspondent and will be following the club from a London base throughout the 2013-14 season. Follow him on Twitter @garryhayes.