Samoan international Nanai-Williams featured in many of their better attacks, snaring a brace and joining Foti Lokotui, Johnny Kawau and Kalolo Tuiloma as second-half tryscorers.
Hawke's Bay had the final say in both halves, with tries to Ash Dixon and Pasqualle Dunn.
However, their injury-laden side will need to reduce their error count considerably if they are to stop the rot and reach the Championship division semi-finals.