Having shown promise but failing to win in the first 10 matches of Merrick's reign, the Phoenix have now emerged victorious in five of their last seven outings and seem set to make a serious run at the finals.
Where Wellington sides of years past were built on a solid rearguard, this side can crackle in possession. The Costa Rican duo were again outstanding after missing last week's loss to Brisbane, while Tyler Boyd was also impressive starting in place of Jeremy Brockie.
After failing to fire at Eden Park in the 1-0 win over Perth and the 1-1 draw with Adelaide, the Auckland public were treated with Wellington's new brand of attacking football in a lively first half. They led by two at the break and it could've been more but for a combination of some inaccurate finishing and questionable calls from the linesman.
Wellington started brightly and Stein Huysegems really should have scored when he was put clean through by a brilliant ball from Hernandez. Barely a minute later, though, the Phoenix were in front.
Adelaide's defence failed to clear following Eugene Galekovic's one-on-one save and, after Hernandez was barged over in the box, he coolly slotted the resulting penalty.
The Phoenix were getting behind the Adelaide defence with relative ease but, 10 minutes after the goal, they somehow failed to add to their advantage, when Huysegems hit the post with his left foot and the bar with his right in the space of a second.
The second goal their football deserved finally arrived just before the break, courtesy of the Costa Rican connection. Hernandez was the supplier and his perfect pass allowed Cunningham to advance into the box, jink onto his right foot and unleash an unstoppable strike inside the far post.
Adelaide had a gilt-edged chance to pull one back shortly after halftime but former Phoenix man Jon McKain, hardly known for his finishing, applied what resembled a defensive clearance when a free kick fell to him in front of goal.
The squandered opportunity appeared to invigorate Adelaide, bossing much of the second spell but unable to find the goal they needed to get back in the game.
Merrick looked to the bench to turn the tide but Brockie couldn't convert two decent chances late on. Fortunately for the Phoenix, the final whistle sounded shortly after Awer Mabil bundled home a consolation goal.
Wellington Phoenix 2 (Hernandez 21, Cunningham 45)
Adelaide United 1 (Mabil 90)
HT: 2-0
