West Brom's high press and repeated box entries meet a Millwall side that can stay compact and attack the space behind. Both sides have a way to reach the first chance. The deciding sequence is likely to be the clearance and the next accurate shot.
Price has been able to release Morgan and Horn Myhre through open play and from short set-piece phases. West Brom generated roughly two expected goals in each of its last three games. Millwall's Derby burst came against loose early spacing, while its next two away attacks produced few shots on target.
Campbell left West Brom's last match injured, and Phillips played the other half; that changes the home defence's response to Lisbie and Cundle. Millwall's Crama and Leonard missed Birmingham and are confirmed unavailable, leaving Osei-Tutu in the right-sided role he played throughout that match. West Brom can test that flank and collect another ball in front of Cooper and Taylor.
West Brom's Southampton first half showed how its pressure can hold an opponent away from goal. I expect Price, Morgan and Horn Myhre to make the later clean chance after the first challenge. That's why I'm siding with West Brom to win.