Sunderland are heading to Wembley for the second time this season after an exceptional rearguard at Fratton Park.
Jon McLaughlin made some good saves but the away side kept Portsmouth at arm's length for the most part and secured the crucial clean sheet they required.
They will face Charlton Athletic or Doncaster Rovers at Wembley next Sunday for an opportunity to bounce straight back into the Championship.
The early exchanges unsurprisingly saw both sides try and edge their way into their contest, particularly given the two selections that had left plenty of firepower on the bench.
Kenny Jackett dropped both Jamal Lowe and Ronan Curtis to the bench, while Jack Ross, still missing Aiden McGeady, recalled Chris Maguire and Grant Leadbitter.
It was the Black Cats who started the brighter, Leadbitter forcing an early save from Craig MacGillivray as he curled a long-range effort at goal after racing onto a long ball.
Sunderland continued to threaten and were unfortunate to see Lee Cattermole steer a dangerous cross from Bryan Oviedo wide of the far post.
The home side started with a clear aim to get the ball in behind the Sunderland defence at the first opportunity, going direct to target man Oli Hawkins.
The atmosphere was fevered but their quality lacking, the Black Cats generally comfortable.
There has been clear ill-feeling between these two sides after four tense games this season, and so it was little surprise that referee Peter Bankes was as busy as anyone in the early exchanges.
Gareth Evans saw yellow for a high boot on Lee Cattermole, while Tom Naylor suffered the same fate after an off-ball exchange with Maguire.
The pair had battled for the ball near the corner flag and as the pair moved away, Naylor threw the ball at the lively Maguire.
Sunderland's first-leg hero saw yellow himself after slipping over near his own box, taking out Nathan Thompson in the process.
Both sides were lacking a touch of composure on the ball, but Portsmouth were limited to long-range efforts from Ben Close and Evans that did not test Jon McLaughlin.
The first real notice of their threat came when Brett Pitman tried a delicate chip to the back post, Oli Hawkins just unable to connect.
Slowly but surely they were beginning to exert some pressure, thought the Black Cats should have gone ahead when Leadbitter sprang Maguire free with a clever early pass. Maguire beat MacGillivray with his first touch but just as he looked set to strike, slipped over again and the danger passed.
Despite that effort the momentum was turning and Jon McLaughlin had to make an exceptional strike as Evans raced onto a Pitman header, the Scot blocking from a matter of yards.
Matt Clarke nodded the resulting corner onto the bar as the Black Cats went into the break under pressure.
That interval served them well and they went close within moments of the restart, Oviedo racing onto a loose ball and firing a half volley just over the bar.
Jackett was forced to act quickly, throwing on top scorer Lowe. The home side went close when Lee Brown built a good overlap on the left, crossing for Hawkins who forced a smart stop from McLaughlin.
Hawkins had some bright moments but struggled as the game went on, and as the frustration in the home stands grew Jackett turned to former Black Cats striker James Vaughan.
The substitute should have scored almost immediately, McLaughlin saving his header after a fine cross for Lowe.
At that stage the Black Cats looked nervy but from there they applied themselves superbly.
Fratton Park went flat as Sunderland held the up the ball up the pitch effectively, killing time as the final whistle.
They saw six minutes of stoppage time through with ease to book their place in the play-off final.
Sunderland XI: McLaughlin; O'Nien, Ozturk, Flanagan, Oviedo; Leadbitter, Cattermole, Power (Morgan, 78), Honeyman; Maguire (Gooch, 67), Wyke (Grigg, 82)
Subs: Ruiter, Dunne, Morgan, Watmore, Matthews
Portsmouth XI: MacGillivray; Thompson, Clarke, Burgess, Brown; Close, Naylor; Evans, Pitman, Solomon-Otabor (Lowe, 52) ; Hawkins (Vaughan, 67)
Subs: Bass, Walkes, Curtis, Dennis, Morris
Bookings: Evans, 3 Naylor, 10 Maguire, 20 Pitman, 45 O'Nien, 75 Vaughan, 78
Attendance: 18,077 (1,397 away)