Rafael Nadal advanced to the French Open final after Alexander Zverev suffered a horror injury blow almost two sets into a gruelling semi-final on Court Philippe-Chatrier.

Zverev was helped from the clay in a wheelchair before returning on crutches to retire, having gone over on his ankle as he was taken to a second-set tie-break after Nadal claimed the first set 7-6 (10-8).

Having been out on court for over three hours despite not finishing two sets in a demanding encounter, Nadal secured a clash with either Casper Ruud or Marin Cilic in Sunday's final as he bids for a record-extending 14th Roland Garros title.

Zverev made an ideal start when breaking Nadal's service in the first game of the match, but Spain's king of clay hit back in the eighth game of the opener, eventually winning a fiercely competitive tie-break to conclude a draining 91-minute set.

Nadal struggled to build on that success in a bizarre opening to the second set, which opened with four consecutive breaks as the Spaniard failed to win a single first-serve point until his third service game.

Having been broken again to go 4-2 down, Nadal made light of any suggestion he was feeling the effects of his four-set quarter-final win over Novak Djokovic, roaring back with another break as Zverev cut a frustrated figure, arguing with the umpire after being warned for shouting an obscenity.

Worse was to come for Zverev during the exact point at which Nadal forced another tie-break, with the third seed left crying out on the clay after appearing to roll his ankle while chasing the Spaniard's forehand.

Having been helped into a wheelchair to exit the court, a distraught Zverev returned on crutches to thank the umpire after a short interlude. That meant Nadal progressed to his 14th Roland Garros final on his 36th birthday, although not in the circumstances he might have imagined, and the 21-time grand slam winner cut a subdued figure as he wished his opponent a speedy recovery.

"It's very tough and very sad for him, he was playing an unbelievable tournament, he's a very good colleague on the tour," Nadal said of Zverev.

"I know how much he's fighting to win a grand slam, and for this moment he was very unlucky. The only thing I am sure of is that he's going to win not one but many more. So, I wish him all the best and a fast recovery.

"It was a super tough match, three hours and we didn't even finish the second set. It's one of the biggest challenges on the tour today to play against him when he's playing at such a high level.

"For me, everybody knows, to be in the final one more time, it's a dream."

Data Slam: 30-up for Nadal as the king of clay closes on another success

Nadal's victory, while arriving in less-than-ideal circumstances, made him just the third player in the Open Era to have reached 30 grand slam finals. Nadal has won each of his previous 13 Roland Garros finals, though he still trails both Novak Djokovic and Roger Federer for overall major finals (both 31).

WINNERS/UNFORCED ERRORS

Nadal 21/26
Zverev 40/47

ACES/DOUBLE FAULTS

Nadal 3/1
Zverev 5/8

BREAK POINTS WON

Nadal 5/11
Zverev 5/8