Rafael Nadal will face Albert Ramos-Vinolas in an all-Spanish Monte-Carlo Masters final after the defending champion beat David Goffin in a semi-final that turned on a poor decision from the umpire.

Fourth seed Nadal will be a strong favourite to win an astonishing 10th title at the Monte Carlo Country Club on Sunday following a 6-3 6-1 victory over Goffin.

But it may have been a different story if 10th seed Goffin had not been the victim of a dreadful mistake from the chair umpire, who came down to inspect a mark in the clay but got the wrong spot on the court and called a shot from Nadal in when it was clearly out.

Goffin would have led 4-2 if the correct call was made, but was clearly affected by that injustice and Nadal took advantage by winning four games in a row to take the first set and dominated the second to reach yet another final.

Belgian Goffin made a blistering start in his quarter-final victory over Novak Djokovic on Friday and led Nadal 2-1 with a break after the man known as 'King of Clay' netted a forehand in the first meeting between the two.

A slick Goffin was brimming with confidence, but he had the wind taken out of his sails when the chair umpire made a gaffe which proved to be costly and prompted the crowd to voice their disapproval in no uncertain terms.

Goffin looked stunned and was rattled as Nadal turned the tide to wrap up a set he should have been just two games away from losing.

Jeers from the spectators continued in a strange semi-final, but Nadal stayed focused on the job in hand and produced some high-quality winners to take charge as Goffin's unforced errors mounted.

Fourteen-time grand slam champion Nadal raced into a 5-1 lead and broke for a third time in the second set with a rasping forehand winner to stand on the brink of being the first man in the Open Era to win a tournament 10 times.