Mullin needed just 16 seconds to fire Wrexham ahead at the New York Stadium. Wrexham's talisman fired home a cross by Ryan Barnett to give the visitors the perfect start. An entertaining first half saw Rotherham press hard for an equaliser but they were denied by some solid Wrexham defending. Goalkeeper Arthur Okonkwo saved from Joe Rafferty and Christ Tiehi and then did brilliantly to keep out a Joe Powell free-kick that took a flick off a Wrexham head.
More chances flowed after the break with James McClean going close for the visitors and Mullin testing Cameron Dawson in the Rotherham goal. Yet Mallik Wilks was causing Wrexham problems and forced Okonkwo to turn a shot behind. The Wrexham stopper also denied Cohen Bramall late on to preserve his clean sheet and ensure the Welsh side head back home with all three points.