Sunderland will play Wycombe in the League One play-off final after Patrick Roberts' stoppage-time goal at Sheffield Wednesday.
The Black Cats had led 1-0 from the first leg but Lee Gregory wiped out their advantage in the second half.
Wednesday then looked the more likely to go on and get a second but the Wearsiders caught them cold.
Jack Clarke escaped down the left and pulled the ball back for Roberts to crash a shot home.
Wednesday still had time to find a second goal that would have sent the tie to extra time because of the 10 minutes that were added on following Sam Hutchinson's head injury earlier in the second half - but they could not fashion one more big chance.