The Latics clash with the Championship outfit in the FA Cup semi-final at Wembley on Saturday and although they are favoured to win, Boyce insists they are not going to ease off just because their South London opponents compete in a lower division.
"We're not going to underestimate Millwall," he said.
"They'll go into the semi-final thinking they've got a great chance of beating us so we've got to go there and put in a professional performance and it's going to be a hard game no matter what.
"It's up to us to take the game to them and get the result that we need. For the first time probably all the pressure's on Wigan."