SERENA Williams said it had been an honour to witness Rafa Nadal's tennis journey and that he would leave the game a "lasting legacy" following the Spaniard's defeat in the final match of his glorious career.

Nadal, who won 22 Grand Slam titles over the course of a career spanning more than two decades, announced his retirement last month and was a surprise pick for Spain's opening singles match in their Davis Cup quarter-final against the Netherlands.

The 38-year-old lost 6-4 6-4 to Botic van de Zandschulp and Spain eventually fell 2-1 to exit the team tournament in Malaga.

"Congratulations on a career that most won't dare to dream of," Williams said on Instagram alongside a video of her wearing Nadal-branded merchandise.

"I feel so fortunate to have been able to play when you were playing and being great.

"You inspired me to be better, to play harder, to fight, to never give up, and to win more. No excuses, just play the sport.

"Your legacy will never die. Wow to see your career from the beginning to today was an honour champ! Long live Rafa!"

Nadal's Davis Cup teammate Carlos Alcaraz said Nadal had been his inspiration.

"Thanks to you I have become a professional tennis player," Alcaraz added.

"It has been a blessing to be able to live your career as a child for whom you were an idol and then as a teammate! The best possible ambassador who leaves an eternal legacy."

World number two Iga Swiatek reacted to a video of the Spaniard tearing up with a crying emoji and said: "Too much", while American Coco Gauff added: "Today, I'm from Spain #Rafa."

Australian tennis great Rod Laver said that watching Nadal compete had been a privilege.

"Your legacy will endure as one of the greatest to ever grace the game," Laver said.

"Thank you for the countless unforgettable moments and for setting a standard of excellence that will inspire generations to come."

German Boris Becker, a six-time Grand Slam champion, said he was crying as he typed out his message on social media.

"What an absolute icon of sport, period! There will never be another one like Rafa! Role model for so many kids all around the world!"