Rafael Nadal overcame Belgium's David Goffin in straight sets to reach the final of the Monte Carlo Masters.
The world number seven had to fight back from a break down in the first set but went on to win it 6-4 in controversial circumstances.
The chair umpire, Cedric Mourier, examined the wrong mark and incorrectly called a long Nadal shot in, which handed the momentum to the Spaniard.
That appeared to frustrate Goffin who then lost 6-1 in the second set.
Nadal said after the match that he was "very happy to be in the final of such an important competition - the first of the season on clay".
"I found a way to create some damage on David because at the beginning of the match he was dominating," he added.
Compatriot Albert Ramos-Vinolas stands between him and his 10th Monaco Masters title in Sunday's final.
"It will certainly be a tough final - Albert has beaten Andy Murray to be here so I will have to play my best to win - he is playing fantastic at the moment".