The 'Nix are in free-fall and caoch Ernie Merrick must be wondering how to snap a winless streak which now stands at nine games.
Four defeats in a row and a sixth loss in their last seven is a horrendous run for a side who haven't won since 5 December, when they beat Melbourne Victory in Auckland.
They looked devoid of creativity, especially with Roly Bonevacia far from his effervescent best, and inexperienced attackers Blake Powell and Joel Stevens had only scraps off which to feed.
A handful of half-chances aside, the Phoenix really didn't trouble Perth, who took advantage of some slack marking to go ahead in the first half.
Nebojsa Marinkovic whipped a ball in from the right and Harold, totally unmarked, headed past Glen Moss to record his fourth goal of the season.
Michael McGlinchey set up Powell late in the first half but his shot was deflected out for a corner, before Ante Covic denied McGlinchey after great work down the right by Louis Fenton.
McGlinchey really should have scored and it was a close as Wellington came to equalising.
Marinkovic's curling shot was fabulously saved by Moss early in the second half, while Andy Keogh, who did the donkey-work up front all afternoon, was only denied by a great recovery tackle by Phoenix defender Dylan Fox.
Merrick threw Matthew Ridenton and Kwabena Appiah into the fray but neither had an impact, with the latter particularly struggling to get past Glory left back Marc Warren.
The win was only Perth's second away win of the season, but a thoroughly deserved one at that.
Wellington Phoenix 0
Perth Glory 1 (Harold 21')
Westpac Stadium, Wellington
Crowd: 7,135
