Hereford's Tom Owen-Evans has opened the scoring at Merstham in the 42nd minute after good work by Harry Pinchard.
Earlier in the half Hereford had several chances with one effort cleared off the line.
Keeper Liburd-Hines has had little to do.
Hereford have had plenty of possession and have looked very fluid at times. But they probably should be more than one goal ahead.
Half-time at a very wet Moatside Stadium:
Merstham 0 Hereford 1