The match was a homecoming for Mertens, but finished in frustration.
“After beating Liverpool, we really should've picked up another three important points here. We only got one and that is a pity," Mertens told Sky Sport Italia.
“It is always nice for me to come back to Belgium, but I wanted the three points. We also wanted to come here and play our football, but the mood in the dressing room will tell you we didn't do that."
Arek Milik wasted several big chances yet again, but Mertens rushed to defend his teammate.
“I've already said, Arek is a great player and we just have to maintain our faith in him. He will be important for this team again. He's proved himself before and will do again."