I thought he started well but then started getting too close to Lukaku. His booking was stupid and when Fernandinho had to bring down Cleverly Mangala didn't need to be that far up field to challenge Lukaku for that header (whether he was actually fouled and it not given or not).
Second half, he was taking a step back, reading the situation. He wasn't getting sucked in by Lukaku and was much better for it.
Played really well second half and actually well for a fair bit of the first half. He will have learnt a lot today from what he saw himself succeed in doing in the second half. Especially after how poor he was at Everton last season when Lukaku dominated him.