Rhys Hanbury went over in the corner to put the a kick behind although this one went unconverted.
Three minutes later Jon Clarke scored the third Widnes try and the conversion by Ah Van put his side four up.
Cameron Phelps then added another try for Widnes that was converted before Richard Owen pulled one back for the hosts.
However, Ah Van went over himself to put Widnes 26-16 up at the break. Then came the Tigers comeback.
Jordan Thompson scored 19 minutes into the second half and with Ellis's conversion the deficit was just four.
Then Adam Milner went over for a try and Ellis held his nerve to kick the hosts two points clear.