Angel di Maria was the most expensive acquisition. The Argentina international cost the Red Devils a cool £60 million - making him the most expensive player in British football history - while Arsenal splashed out £35 million on Sanchez from Barcelona, and Costa cost Chelsea £32 million.
Let’s take a closer look at how the three players - possibly the top three Premier League signings of the summer - have settled, and which one deserves to be labelled ‘signing of the summer’.
Angel di Maria
For the first time since 2009, the year Cristiano Ronaldo left Old Trafford for Real Madrid, Manchester United have a true number seven - a genuine star with the ability to get fans off their seats every time he touches the ball.
Angel di Maria is unquestionably one of the world’s best players - and the Red Devils probably still can’t believe their luck that Real Madrid sold him.
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The Argentina international has enjoyed a steady start to his Manchester United career, scoring three goals and providing six assists in his first 11 matches, but clearly there’s much more to come from the 26-year-old who admits the language barrier has been an issue.
Currently sidelined with a hamstring injury, Di Maria loses points for his disappointing displays against Chelsea and Manchester City, in particular.
One year after smashing their transfer record on Mesut Ozil, Arsenal forked out £35 million on Barcelona’s Alexis Sanchez.
The Chilean has done more for the Gunners in four months than Ozil has done in a year-and-a-half.
With a superb 14 goals in his first 22 appearances, Sanchez has exceeded expectations at the Emirates Stadium. It could even be said that, at times, he’s carried the north London outfit.
An almost perfect start to his Arsenal career, Sanchez narrowly misses out on a 10/10 rating for failing to score or provide an assist in the crunch matches against Chelsea and Manchester United.
There were a few nagging doubts over whether Diego Costa was the right man for Chelsea, but Jose Mourinho knew the Brazil-born Spain international, who flopped at the World Cup finals but was magnificent last season for Atletico Madrid, was the perfect signing for the Blues.
Costa has been sensational at Stamford Bridge, scoring 11 goals in his first 10 Premier League appearances.
The hot-headed striker must learn to keep his cool a little better - it seems a mere matter of time before he’s shown his first red card for Chelsea - while his hamstring problems have let him down on a couple of occasions this season.
However, if he continues his early-season form, Chelsea fans will start to wonder whether Costa could go on to become an even better striker for the Blues than the great Didier Drogba.