It looked to me like he was playing his usual position? Maybe a little further up the pitch but he was playing behind a striker for most of the game.
Atsu started as the central striker, with Perez behind him. They seemed to swap a bit. Then Gayle came on and played as the central striker again with Perez behind him.
Perhaps he had less defensive responsibilities which allowed him to focus on finding space more, which he's always been good at.