The initial exchanges led to sustained pressure by the city hosts but Portadown worked hard to protect the clean sheet.
This bright opening period sparked a positive spell by a Portadown side struggling for points on a return to top-flight hockey.
Leeanne Cassells tested the Harlequins goalkeeper before Abbie McCullough steered a shot the wrong side of the post.
However, individual errors left Portadown on the backfoot as Harlequins moved in front courtesy of a counter-attack late in the first half.
A corner was deflected home to hand Portadown a setback entering the break.
Harlequins increased the advantage with a brace of goals across the opening minutes of the second half.
Emily McStea and Cassells worked hard at the head of the Portadown attack as the visitors enjoyed plenty of possession.
Kim Scott and Esther Dickson also proved impressive but Portadown struggled to turn time on the ball into a return on the scoresheet.
“I cannot fault the application and the players are obviously trying hard to do the right things,” said Jane McKimm, Portadown ladies’ firsts’ head coach. “The desire is obvious but this remains an unforgiving league and it is down to the small margins.”
Portadown ladies’ firsts play host to Ballymoney tonight (Friday) at Edenvilla Park from 8 o’clock.
The club’s thirds lost out to Queen’s by 3-2. The seconds defeated Grosvenor at home as Gaby Silcock grabbed a treble in the 3-1 success.
The latest Ulster Hockey Blitz for the under 11s and under 13s provided games for six town sides against Grosvenor, Pegasus, Victorians, Harlequins, Dungannon and Banbridge.