After Karim Benzema had scored the only goal in Seville in last week's semi-final first leg, Jose Mourinho's side had to deal with some tireless chasing and crunching tackles from a fired up Sevilla before their two German internationals combined to make the vital breakthrough in the 82nd minute.
Sami Khedira's superb pass from central midfield sent Mesut Ozil clear and he rounded goalkeeper Javi Varas to finish into the empty net.
Sevilla defender Sergio Sanchez was dismissed for a second yellow card in the 85th after a late tackle on new loan signing Adebayor, making his debut at the huge arena in central Madrid after joining from Manchester City last month.
The Togolese international had been on the pitch for around 10 minutes when he controlled a Lassana Diarra centre on his chest in added time and volleyed powerfully past Varas from close range to make it 2-0.
"We do not want to speculate about the result," Mourinho said at a news conference when asked about his predictions for the April 20 final.
"History shows that there are never any favourites in finals," the Portuguese added. "It's better to be in a final than not and we deserve to be there."
CRUSHING WIN
A second-string Barca had earlier completed a crushing 8-0 aggregate victory over Almeria, with Adriano, Thiago Alcantara and Ibrahim Afellay scoring in a 3-0 win on the night.
The result means Real, seeking their first domestic Cup since 1993, and Barca, the 2009 winners, will meet in the final for the first time since 1990 when Barca won 2-0.
The final, which has yet to be given a venue, takes place a few days after the great rivals meet in Madrid in the league and they could also be drawn to play each other home and away in April's Champions League quarter-finals.
Barca coach Pep Guardiola left World Player of the Year Lionel Messi and five Spanish World Cup winners out of his starting 11 at Almeria's Juegos Mediterraneos stadium.
Second from bottom in the league, the home side came close to scoring just before the half hour when French midfielder Sofiane Feghouli, who joined on loan from Valencia in the January transfer window, smashed a low shot off the post.
But the Andalusian club, in the last four for the first time, then conceded a soft goal to Barca left-back Adriano in the 35th minute to effectively end any faint comeback hopes.
Teenage midfielder Thiago underlined his potential with a fine header to make it 2-0 in the 56th before Netherlands international Ibrahim Afellay netted his first goal for the club since joining last month from PSV Eindhoven.
"Getting to the final is very tough," Guardiola told a news conference. "We deserve it and the fact we have been there twice in three years says a lot about our players."
Barca are the record King's Cup winners, with 25 from 34 appearances in the final, a much better record than Real, who have won 17 of 36 finals.
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