Keown told BBC Sport: "It was a fantastic team performance but this fella is the icing on the cake. I haven't seen anybody of his quality for years.
"[Thierry] Henry was the last one I saw with this sort of pace and the sort of quality he has. It creates panic in the defence and you just cannot take risks with him.
"Can he link with players as Olivier Giroud does? Yes, of course he can.
"He occupies defenders, Cahill was always looking over his shoulder. He's creating space for others to run into."