Sasa Lukic had canceled out Yoane Wissa's first goal for Newcastle before Miley struck deep into injury-time for the hosts to win 2-1.
Miley started the tie at right-back and Howe enthused afterwards: "I'm reluctant to put more pressure on his shoulders than he's already got, but he can be as good as anyone in his position, whichever position he plays.
"I thought he was outstanding at right-back and he's really grown in central midfield in terms of stature and confidence and belonging, which are all really important qualities - and the goals will only add to that.
"He's got a bit of everything so I couldn't rate him any higher."
Howe added, "He's here on merit, he believes that he's more than good enough to play at this level. Not just play but excel and he's taking his game to another level and I think we're seeing that now."