However, Bradford got back in the game just before the break when Omari Caro intercepted a pass and ran 90 metres to score a try and Addy secured the extras.
In the second half, Widnes quickly restored their advantage when Charly Runciman crossed over the line, and he was soon followed by Mellor for his second score as he collected his own kick over the top to touch down.
Hep Cahill and Ah Van compounded the visitors' advantage as the Bulls' defence began to wilt. Rhys Hanbury put the game beyond any doubt with a score in the 68th minute.
The Vikings continued their assault on the Bradford tryline when Kevin Brown scored their ninth try of the game in the 72nd minute, and Ah Van notched his hat-trick in the dying minutes to complete the dominant victory.