Granted nobody was bad so it's harsh to call him the worst, but he was the least useful in my eyes because he gave possession away the most. That's all I mean by it.I see fernandinho winning the ball very quickly, high up the pitch. Playing with such an attacking formation you need at least one player who can do that.
Yaya is a superior passer, doesn't win the ball back though.
But to say Fern was the "WORST" player is a bit derogatory to his overall performance.