The two Spaniards were involved in a gruelling encounter that lasted more than three hours before Nadal secured a 6-4, 4-6, 6-3 victory at the Indian Wells Tennis Garden in California in the United States.

Alcaraz is almost half the age of the 35-year-old Nadal but pushed the 21-time Grand Slam champion all the way in windy conditions.

The 18-year-old saved 15 of the 20 break points he faced in the opening two sets as he forced Nadal to a decider.

But Nadal crucially converted the only break point he created in the final set as he ensured experience prevailed over youth in a battle of the generations.

"I took it like another semi-final match," said Nadal.

"He's not a young player that is 100 in the world and is coming.

"He is a top player already, so I treated it like that, playing against one of the best players in the world.

"It doesn't matter if he's young or not, he's a great guy, an amazing player and he has a fantastic future.

"I treated it like this, just tried to go on court, try my best and accept all the challenges.

"I am through and it was a very important victory for me."

Nadal has also extended his winning run to 20 matches at the start of the season and is just won victory away from equalling the record for the most Association of Tennis Professionals Masters 1000 titles in history of 37 held by Serbian Novak Djokovic.

"I am super happy to be in the final," said Nadal.

"It means a lot to me, and I'll just keep going."

Fritz will be hoping to stop Nadal in his tracks after securing an impressive 7-5, 6-4 win over Russian seventh seed Andrey Rublev.

Competing as a neutral, Rublev was on a 13-match winning run but came unstuck against Fritz who looked inspired in front of Californian crowd.

Fritz quickly asserted himself in the match, bursting into a 5-2 lead before withstanding a Rublev fightback to take the opening set.

The 24-year-old saved two break points at 4-4 in the second set before holding his serve and capitalising on his first match point in the next game to seal victory.

The Californian is the first man from the US to make the Indian Wells Masters final since John Isner in 2012.

"It doesn't even seem real," said Fritz.

"I'm just trying to take in the moment, regroup and come back tomorrow for the final.

"But it's a dream come true."

Unseeded Xu Yifan and Yang Zhaoxuan of China defeated seventh seeds Asia Muhammad of the US and Ena Shibahara of Japan 7-5, 7-6 to clinch the women's doubles crown.

Americans John Isner and Jack Sock saw off Mexico’s Santiago Gonzalez and France’s Edouard Roger-Vasselin 7-6, 6-3 in the men's doubles final.

Tomorrow is scheduled to see Fritz and Nadal go head-to-head for the men's singles title, while Greece’s Maria Sakkari and Poland’s Iga Świątek meet in the women’s singles final.