Fabregas makes the initial pass to Costa down the left, the ball goes sideways till it ends up back with Fabregas again, he was the only one trying something more than just moving it on throughout that move(and in most of the game so far) and his ball that played Ivanovic in to play the ball across.
Ivanovic is such a good player though, for really a CB with a CB build he is ridiculously good as a fullback, puts in some fantastic balls, is far better than he should be driving forward and he's got a great shot on him. All on top of being a great defensively.