Oxford United ended a goal famine with their first win of the season in front of the television cameras at the Manor Ground.
For the first 25 minutes Portsmouth ran them ragged and only three excellent saves by Phil Whitehead from John Aloisi, John Durnin and David Hillier, kept them in the game.
United, without a goal for 402 minutes at the start of the match, finally found the net after 28 minutes.
Jamie Cook, Paul Powell and Matt Murphy linked up on the left before the ball was played out to Les Robinson whose cross from the right was headed in by England under-21 International Simon Marsh.
Seven minutes later Pompey conceded a penalty and had full back Robbie Pethick sent off.
Cook flicked a pass from Murphy past the full back and was allowed to continue after Pethick pulled at his shirt.
Cook's shot was brilliantly saved by Aaron Flahavan but referee Paul Taylor halted play, awarded Oxford a penalty and red-carded Pethick who had been booked earlier for another foul on Cook.
Dean Windass scored from the spot.
A high ball to Windass brought his second goal and Oxford's third goal 16 minutes from time.
He chested down a ball on the edge of the box before firing home a superb right-foot shot.
It was all Oxford in the second half. They had to reorganise the defence after Phil Gilchrist pulled a hamstring on the stroke of half-time.
But, 60 seconds after Whitehead brilliantly turned a close range shot from Aloisi over the bar, United struck again.
Portsmouth failed to clear on the edge of their penalty area and Murphy slipped a high pass to Dean.