Hawkes Bay, with a raft of first-choice players unavailable, took a long time to warm to their work. No 8 Joseph Penetito again carried strongly, scoring two tries, while fellow loose forward Tony Lamborn finished a sterling break by wing Mason Emerson.
One of the main features of the Magpies pack was that lock Junior Waqa carries the ball like it's a load of bread.
The score was 12-9 until Penetito's second on the stroke of halftime.
The expected second half points avalanche never really materialised. Indeed, Hawkes Bay kicked just four penalty goals, two of which came when Fox was sinbinned, and scored three late tries, one to wing Shannan Chase, set up by fullback Zac Guildford, to inflate the scoreboard.
If only 'Nua No 10 Hamish Buick had latched onto an intercept for an early try. He did make up for it with a superb chip and regather which set up the unlikely named wing Teegan Minkley, whose bust led to a try to No 8 Sam Gardner.
At 20-16, it was game on.
Hawkes Bay's next defence is against Meads Cup champions Mid Canterbury next Thursday in Napier.
Hawkes Bay 50 (Joseph Penetito 2, Tony Lamborn, Shannan Chase, Tom Stanley, Mark Braidwood tries; Tyrone Elkington-MacDonald 4 con, 4 pen)
Horowhenua Kapiti 16 (Sam Gardner try; Perry Hayman con, 3 pen) Halftime: 17-9