But without star striker Andy Carroll, who withdrew yesterday morning with an ankle injury, the Hammers looked blunt upfront and will be hoping new Ecuador striker Enner Valencia will add some firepower when he finally joins up with the club.
The Phoenix made the gulf between the A-League and the English Premier League seem miniscule in the first half when Andrew Durante nodded home an open header from an Alex Gorrin freekick in the 11th minute.
Eleven minutes later the former Sunderland U-21 skipper doubled the lead when he was allowed to travel unopposed to the edge of the West Ham box, before rifling home a low right footed strike into the bottom corner.
It was a dream debut for the 21-year-old striker who is a defensive midfielder by trade, but showed a clinical cutting edge in the box that was missing last year.
Substitute Mauro Zarate pulled a goal back for West Ham in the 71st minute, curling a shot into the top corner from the edge of the box.
Merrick described the performance as 'crucial.'
"It was the ability to win the ball and keep it which made me happy," Merrick said. "We were never going to progress in the A-League by playing long balls to Jeremy (Brockie) up there on his own. Our real strength was a rock solid back line and we were well protected by a bank of midfielders.
"At halftime I said 'look, you're going to get beaten, don't worry about it when the goals go in just keep playing football."
The Phoenix don't start their season until October, but they have plenty to be excited about for the new campaign. Last season's player of the year Albert Riera picked up man of the match and looked back to his composed best in the middle of midfield, while new Australian signing Nathan Burns looked a handful going forward.
West Ham skipper Winston Reid had a quiet night, but felt the brunt of a few hard tackles, as the Phoenix players threw everything at the visitors.
"I was disappointed with some of the tackles that went on in the first half, the referee should have done more and let the game get out of control for a while there," said Allardyce.
In response Merrick said he thought the referee was brilliant.
The crowd of 19,183 was less than the 21,000 the Phoenix board needed to break even.
Wellington Phoenx 2 (Andrew Durante, Alex Gorrin)
West Ham United 1 (Mauro Zarate)
HT 2-0.