Radamel Falcao scored the only goal of the game as Monaco set up a Coupe de la Ligue final against holders Paris Saint-Germain by beating Nancy 1-0 in a tight last-four clash at Stade Louis II on Wednesday.
It was far from a fluent performance from the Ligue 1 leaders, who had lost the last three times they had appeared in the semi-finals, but they scrapped their way to a narrow victory.
Falcao gave Monaco the lead just before half-time, the Colombia striker making the most of a costly mistake by Nancy goalkeeper Guy N'Dy Assembe to head home.
Monaco have only lost one domestic game at home all season and they looked assured enough in their lead despite the visitors creating a number of good openings.
Julien Cetout and Antony Robic wasted the best of Nancy's chances, the former prodding just wide after incisive build-up play sent him clear on goal while the latter sliced an effort over the crossbar.
Monaco held out for the win, though, and face PSG in the final on April 1, while they also play Unai Emery's men in a potentially decisive league match in the capital on Sunday.
Issiar Dia pulled a shot wide from the right of the penalty area in the third minute as Nancy made a strong start.
Chances proved at a premium in the opening half hour in front of a sparse crowd, though, with Anthony Koura seeing a tame shot easily saved by Monaco goalkeeper Danijel Subasic.
Maurice Dale shot wide after being sent through by Dia, before Falcao was off target for Monaco with an ambitious diving header from Djibril Sidibe's cross.
Monaco, playing their seventh Coupe de la Ligue semi-final, cranked up the pressure and Assembe saved Kylian Mbappe-Lottin's shot with his legs before tipping Thomas Lemar's vicious free-kick over the crossbar.
But the goalkeeper made a huge error to gift Monaco the lead in first-half stoppage time.
Jemerson's hopeful flick into the box was completely misjudged by the Cameroonian and Falcao stole in behind him to guide a header into the unguarded goal.
Assembe prevented Monaco from doubling their lead shortly after half-time, however, palming Sidibe's strike around the post after Bernardo Silva won the ball back on the edge of the box.
Koura and Cetout both missed good chances for Nancy as the visitors pressed for an equaliser, the latter poking wide after a superb one-two with Dale.
Falcao headed Lemar's centre wide after 70 minutes with Monaco looking to make the game safe, before Subasic saved from Tobias Badila.
Monaco needed penalties to squeeze past Sochaux in the last round and Nancy should have levelled the tie with 10 minutes to go.
Faitout Maouassa burst down the left and pulled back a low cross for fellow substitute Antony Robic, who screwed his shot over the crossbar from six yards out when it looked easier to score and that proved costly as Monaco saw out the remainder of the game to seal their progression.
