Chelsea have confirmed the signing of Willian from Anzhi Makhachkala for a reported fee of £32million.
The 25-year-old playmaker, capped twice by Brazil, has been granted a work permit to complete his move from Russian club Anzhi Makhachkala after agreeing a five-year contract with the Blues.
"I'm very happy to be here, it's been a dream of mine to come and play here," Willian said on Chelsea's official website.
"Chelsea are one of the best clubs in the world and now I'm going to play for one of the best managers in the world. I'm very happy and looking forward to it."
Willian, who will wear the number 22 shirt, looked set to join Tottenham only for Chelsea to hijack the deal and outbid their Barclays Premier League rivals.
He had passed a medical at Spurs before Mourinho swooped to add him to Chelsea's attacking options.
Persistently linked with a move to England, he spent six years at Shakhtar Donetsk where he made his name as a creative midfielder player before joining Anzhi in January.
He began his career in his homeland with Corinthians before moving to Europe with Shakhtar Donetsk in 2007. He made over 100 appearances for the Ukrainian club before moving to Anzhi.