Chelsea have completed the signing of Willian from Anzhi Makhachkala on a five-year contract.
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Last week, the 25-year-old Brazil international looked set to join Tottenham after undergoing a medical with the club, only for their London rivals to move late for his signature.
The Blues confirmed on Sunday that a deal was in place to land the forward, subject to a work permit -- which was granted on Wednesday to allow the move to be sealed.
Willian told Chelsea's official website: "When the offer came, I never gave a thought to anybody else. I said to myself that I would run here, and I'm happy to be here now. Chelsea was always my first choice.
"It's going to be an immense pleasure to work with Jose Mourinho, listen to him and learn from him. I'm sure I'm going to grow as a professional, and I'm looking forward to training.
"He's one of the best coaches in the world with everything he's won. I'm sure I'm going to learn a lot and improve a lot.
"My style is that I like to dribble a lot and play with speed. I like to accelerate very fast with the ball. I'm also quite technical -- I like to shoot at goal, but I've also learnt to defend, which is something you have to do to help the team.
"I intend to help the team as much as I can in order to be successful. I want to train hard, work hard and give everything to earn my place in the side."
Willian signed for Anzhi from Shakhtar Donetsk in January after spending six years with the Ukrainian club, having joined them from Corinthians in 2007.
The attacking midfielder has two caps for his country, with Chelsea now boasting six Brazilian players in their squad.