NI were hoping for a quick start like they produced in their win against Romania last time out.
They were returning to Seaview for the first time since October 2023, a stadium that had served them so well in the past, but their start mirrored the one they made in Gdansk as they found themselves 2-0 down after 10 minutes.
Pajor nearly scored after just 40 seconds as she lifted the ball over the onrushing Jackie Burns but her effort bounced just over the crossbar.
The striker was not to be denied on five minutes as she prodded home from Martyna Wiankowska's cross.
She doubled her and Poland's tally on nine minutes, capitalising on an error from Burns.
The goalkeeper was caught in possession on the edge of the box and Pajor nipped in to dispossess her before rolling the ball into an empty net for her 68th international goal.
Tomasiak smashed home a fine third from close range on 27 minutes as the ball fell kindly for her in the box after Northern Ireland failed to clear their lines.
Simone Magill was the one bright spark for NI in a tough first half, but her shot from a narrow angle was blocked by Wiktoria Zieniewicz.
Burns was then forced to thwart Tomasiak and Natalia Padilla, with Oxtoby's side relieved to hear the half-time whistle.