Chelsea have confirmed the signing of attacking midfielder Willian from Anzhi Makhachkala on a five-year deal after he was granted a work permit.
The Blues are believed to have paid £30m for the Brazil international, 25.
"Chelsea are one of the world's best clubs and now I'm going to play for one of the world's best managers," he said.
Willian had been close to joining Tottenham after having a medical last Wednesday only for Chelsea's Russian owner Roman Abramovich to intervene.
His fellow Russian oligarch Suleyman Kerimov owns Anzhi and it is understood the Blues made their move at around 18:00 BST on Thursday, with a fee and personal terms agreed within 24 hours.
"I'm very happy to be here, it's been a dream of mine to come and play here," Willian, who will wear the number 22 shirt, added.
Sources close to the player said Chelsea have made enquiries or offers for his services in every transfer window since 2011.
On Friday Blues manager Jose Mourinho had indicated that Willian would choose Chelsea over Tottenham.
Willian joined Anzhi in January for a reported £30m after five-and-a-half seasons with Shakhtar Donetsk in Ukraine, but he became available as the Russian club attempt to cut costs after a change in strategy by their owner.
Tottenham had expected to break their transfer record and make Willian their fifth major summer signing.
Willian's arrival at Stamford Bridge further strengthens a squad full of attack-minded midfielders including Eden Hazard, Oscar, Kevin De Bruyne, Schurrle and Juan Mata, who Mourinho insists will not be leaving.