Former Derry City striker Ronan Curtis bagged the opening goal but Portsmouth were held in the first leg of their League One play-off semi-final against Oxford United.
The Republic of Ireland forward pounced to give Pompey the lead in the 32nd minute at Fratton Park.
However, it was short-lived as the visitors levelled 11 minutes later.
Marcus Brown was the man who grabbed the goal, collecting the ball and running forwards before hammering home a shot past Alex Bass.
Former Glenavon midfielder Mark Sykes had to be content with a place on the Oxford bench but made his bow 10 minutes after the restart.
Sykes, who has been in the Northern Ireland squad, replaced Ben Woodburn and looked lively. He put the Portsmouth defence under pressure but neither side could add to their tally.
They meet again on Monday evening with Oxford feeling they will be in the driving seat with home advantage to come.
Curtis claimed he was fouled by Oxford substitute Daniel Agyei in second-half stoppage time.
"We have waited three months for this game and were unlucky," he said. "We battered them the whole game and deserved more but the referee and the linesmen did not help us."
Sykes' Northern Ireland team-mate Paul Smyth, meanwhile, was an unused sub as his Wycombe Wanderers side hammered nine-man Fleetwood Town 4-1 in the other semi-final first leg, with Nnamdi Ofoborh, Alex Cairns (own goal), David Wheeler and Alex Samuels on the scoresheet.