Kaiserslautern failed to have a single effort on target in the first half at the Ludwigsparkstadion, but were a different side in the second period to book their place in May's final in Berlin thanks to goals from Marlon Ritter and Almamy Toure.
Runaway Bundesliga leaders Bayer Leverkusen face Dusseldorf in the second semi-final on Wednesday.
Third-tier Saarbrucken had claimed some huge scalps on their way to the last four, dumping reigning Bundesliga champions Bayern Munich out in the second round before earning a 2-0 victory over Eintracht Frankfurt.
Their quarter-final against Borussia Monchengladbach saw them snatch victory with another late goal, this time from Kai Brunker in the third minute of added time.
However, Brunker was unable to reproduce such heroics in the semi-final, firstly heading straight at visiting goalkeeper Robin Himmelmann and then failing to get his diving header on target from a Marcel Gaus free-kick.
Saarbrucken goalkeeper Tim Schreiber was called into action for the first time in the 48th minute as he comfortably saved a 25-yard shot from Filip Kaloc, but the 21-year-old then committed a costly error to gift Kaiserslautern the lead.
Ritter's glancing header from Toure's cross appeared to lack the power to trouble Schreiber, only for the ball to somehow go through the goalkeeper's legs at the near post.
Toure doubled his side's lead on 75 minutes with a far better header into the far corner from Tymoteusz Puchacz's inswinging free-kick and that always looked enough to seal victory for Friedhelm Funkel's side.
Saarbrucken pushed forward in search of the goal needed to get them back into the tie but Brunker's miserable night in front of goal was summed up when he blazed a half-volley over the bar from close range and beat the ground with his fists in frustration.
It is the first time Kaiserslautern have reached the final of the DFB-Pokal since 2003 – when they lost to Bayern Munich – and they will be massive underdogs if, as expected, Xabi Alonso's unbeaten Leverkusen side are their opponents.
However, Kaiserslautern's route to the final four did include a 3-2 win against top-flight opponents Cologne in the second round before victories over Bundesliga 2 rivals FC Nuremberg and Hertha BSC.
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