The west London side agreed a fee with Atletico Madrid on Tuesday evening, with Chelsea paying a reported £32m to activate the Spain international’s contract release clause.
Costa scored 27 goals in 35 appearances as los Rojiblancos won La Liga on the final day of the season, whilst third-placed Chelsea scored 31 goal less than champions Manchester City.
And former Liverpool and Manchester United striker Owen feels Jose Mourinho would have secured his third Premier League title had the Portuguese coach had Costa during the 2013/14 campaign.
Quiet World Cup but Diego Costa is a great signing for Chelsea. They'd be current Premier League Champions if they had him last season.
— michael owen (@themichaelowen) July 1, 2014
MORE: Man United latest news
MORE: Arsenal latest news
MORE: Chelsea latest news
MORE: Liverpool latest news