And Powell, a 24-year-old in his maiden campaign in Wellington, had scored only three goals in 15 appearances, taking more than four hours between strikes this season.
But, as happens so often in football, that all counted for nought as the Phoenix exhibited a clinical edge that had been lacking throughout their disappointing year. They will still struggle to make the playoffs, remaining in ninth and sitting eight points outside the top six, but they at least now have one hell of a season highlight.
Merrick installed a canny gameplan for playing away from home against a superior side, with the Phoenix ceding a vast majority of possession but largely frustrating their opponents in the middle third. They rode their luck a little, particularly early in the first half, as a combination of desperate defending, wayward finishing and two timely saves from Glen Moss kept their sheet clean until Mitch Nicholls and Mark Bridge grabbed late consolation.
But Powell's brilliance meant it was hard to quibble with the final result, even if the Wanderers would have been left ruing their inaccuracy in front of goal.
Western Sydney needed only watch Powell's first half to be reminded of the value in seizing opportunities when presented. The striker enjoyed three chances and took three goals, each more spectacular than the last.
Seemingly possessed by the spirit of Zlatan Ibrahimovic, Powell had the Phoenix in front with a smart diving header, doubled their lead with a fierce half-volley and put his side firmly in control with a wonderful lob.
The third, in particular, was jaw-dropping, with Powell showing equal parts composure and panache to lob the onrushing Andrew Redmayne from an acute angle. Powell's first two, meanwhile, came courtesy of Tom Doyle's pinpoint crossing from the left, with the fullback unfortunate to be forced off through injury after enjoying a fine first 45 minutes.
While it could have been 3-3 at the break but for the home side's profligacy, that worried Wellington little as Moss' feet and Powell's head helped make it 4-0 midway through the second spell. And, after the Phoenix defence was breached, Michael McGlinchey's penalty saw Wanderers ship five goals at home for the first time in their history.
Wanderers 2 (Nichols 75, Bridge 84)
Phoenix 5 (Powell 4, 20, 33, 71, McGlinchey 90)
HT: 0-3