Sunderland survived a testing 20 minutes with ten men to take a narrow lead to Fratton Park next Thursday.
The Black Cats had looked set to finish the game in the driving seat when substitute Chris Maguire thumped home a glorious volley, but a controversial red shown to Alim Ozturk turned the game on its head.
Portsmouth pushed hard for an equaliser but the home side defended well and were more than worthy of their narrow lead.
It leaves the tie finely posed ahead of the second leg next week.
Neither side had approached the game with much confidence after a disappointing end to the season, and a flurry of injury setbacks had only heightened the lack of fluidity to the play of both teams.
Portsmouth were lacking the attacking threat of Brett Pitman and at left-back, regular Lee Brown had to be replaced by Anton Walkes, a naturally right-sided player.
That may have come as a boost to Sunderland but just fifteen minutes before kick off they were rocked by an ever bigger blow, Aiden McGeady forced to drop out of the squad altogether. Lewis Morgan was pushed onto the left flank with Lynden Gooch coming into the starting XI.
The impact on Sunderland was obvious, the home side set up to exploit the wide areas but unable to do so.
They did threaten briefly in the early stages, Lee Cattermole getting a run on his marker from a corner and flicking on a header. It might have brought a goal for Alim Ozturk but a deflection from the Portsmouth defence just took the ball away from danger.
Though both sides looked to commit runners on the break, it was a cagey affair with neither goalkeeper troubled.
Kenny Jackett's side made an early change in switching their two wingers, Ronan Curtis badly struggling for form and Jamal Lowe quieter than usual.
Though Charlie Wyke was often too isolated leading the line, it was the Black Cats who caused the most problems.
Wyke perhaps could have done better when Lynden Gooch put in a good early cross from the right, the target man just mistiming his leap and nodding harmlessly wide.
He went much closer ten minutes later when Sunderland worked a good overlap on the right, Max Power rushing onto a pass and crossing into the box. Wyke met it on the bounce but under pressure from the defender, fired well over.
It said much for the half that when Craig MacGillivray easily gathered Gooch's long-range effort a minute before the interval, it was the first shot on target.
Sunderland began the second half on top and came close shortly after Ross made an early change, Chris Maguire replacing Morgan.
Maguire quickly freed Gooch down the left, who did brilliantly to get free of Thompson and cross. George Honeyman had made a good run to the near post and connected well with his header, MacGillivray doing remarkably well to block with his face as he leapt in the air.
Decibel levels were rising and the pressure told just moments later as the Black Cats won the ball in midfield. Honeyman moved it out to Oviedo, who crossed deep into the Pompey box. Matt Clarke won the header but Maguire had intelligently dropped to the edge of the area, where he thumped home a wonderful volley.
Sunderland were completely on top but the momentum of the game, seemingly only going in one direction, swung wildly when referee Anthony Woolmer showed a red card to Alim Ozturk.
The home side had worked a clever overlap on the right but Clarke did superbly to cut out a cutback from Luke O'Nien. The centre back continued his run forward and with O'Nien scrambling back, released Gareth Evans into space.
Ozturk tried to make a covering challenge but brought the midfielder down, Woolmer opting for red though the ball seemed to be moving away from goal.
A rattled Black Cats side could only watch as Evans smashed the resulting free kick off the cross bar. From the resulting corner, O'Nien had to block just in front of goal as substitute Omar Bogle turned a loose ball towards the net.
Pompey were in the ascednancy, Clarke a threat as he looked to exploit the extra space by driving forward from the back.
Sunderland broke cleverly, though, and were inches away from a remarkable second when a loose ball from the back was hoovered up by Maguire. He drove towards goal and with Power overlapping on the left, drove a low effort onto the foot of the post.
Ross' side understandably gave up possession for the majority of the closing stages, but contained Portsmouth superbly and stopped them from playing in any dangerous areas.
Jon McLaughlin was left without a save to make as the Black Cats took a narrow but crucial lead.
Sunderland XI: McLaughlin; O'Nien, Ozturk, Flanagan, Oviedo; Cattermole, Power, Honeyman; Morgan (Maguire, 57), Gooch (Dunne 69), Wyke
Subs: Grigg, Ruiter, Matthews, Leadbitter, Hume
Portsmouth XI: MacGillivray; Thompson, Clarke, Burgess, Walkes; Close, Naylor; Lowe, Evans, Curtis (Bogle, 69) ; Hawkins (Solomon-Otabor, 68)
Subs: Bass, Cannon, Morris, May, Dennis
Bookings: Honeyman, 81
Red Card: Ozturk, 69