Marcos Urena, the 32-year-old striker who was part of Costa Rica's squad at the last World Cup, gave the hosts an early lead.
That alone was ominous, given the Phoenix have lost every game in which they have trailed this season — this match followed that trend for the eighth time.
Nkololo bent in a superbly-placed shot from the corner of the penalty area after taking a 24th-minute short corner to give the hosts a 2-0 lead at the break.
Central Coast netted their third to effectively wrap up the three points 10 minutes into the second half when Fenton was adjudged to have fouled Lewis Miller. Replays were inconclusive as Fenton protested his innocence.
Jason Cummings — who missed a match-winning penalty in his last outing — scored from the spot and the commentators were delving into the record books to find Central Coast's largest winning margin in this fixture: 5-0.
They got there in the end. Seventeen-year-old substitute Garang Kuol added a fourth — his first in the A-League — from an embarrassingly simple long ball over the top in the 68th minute.
And Matt Hatch scored in injury time after his initial shot was saved by Oli Sail. But for Sail, this would have been a record defeat — the keeper made several sharp saves and was the only Phoenix player to emerge with much credit.
The Mariners were more threatening throughout, while the Phoenix were laboured and again fell away badly as the score blew out.
Central Coast had 10 shots on target to Wellington's none. David Ball came closest when hist first-half header from a Gael Sandoval free kick glanced off the crossbar.
Riley Bidois made his A-League debut off the bench for the Phoenix as Ball limped off with what coach Ufuk Talay will be desperately hoping is nothing serious.
This was another performance and result to forget for the Phoenix, who are somehow still only one point outside the top six with games in hand on five of the sides above them.
But they have now conceded the most goals and have the worst goal difference in the A-League and look a long way off playoff material on current form.
Central Coast Mariners 5 (Marcos Urena 6 pen, Beni Nkololo 24, Jason Cummings 55 pen, Garang Kuol 68, Matt Hatch 90+4)
Wellington Phoenix 0
Halftime: 2-0
