Alcaraz faced fellow Spaniard Albert Ramos Viñolas and appeared to be maintaining his stunning form with a routine 6-1 win in the opening set.

Yet the 19-year-old was stung by Ramos Viñolas - 15 years his senior - who won the next two sets to leave Alcaraz on the verge of an early exit.

Alcaraz saved match point in set four to take it via a tiebreak, before completing a heart-stopping 6-1, 6-7, 5-7, 7-6, 6-4, win by digging himself out of a three-game deficit in the deciding set.

It took Alcaraz 4 hours and 34 minutes to secure passage into round three, where American Sebastian Korda awaits.

"It has been a great battle against Albert," Alcaraz reflected.

"I knew that it was going to be a great match, tough match. 

"We fought until the last point."

Germany's Zverev was two sets down versus Argentinian Sebastian Baez and faced a match point in the fifth set, but emerged a 2-6, 4-6, 6-1, 6-2, 7-5 winner.

Zverev reached the semi-finals at Roland Garros in 2021 - his best run to date and one of four Grand Slam final-four appearances.

Rafael Nadal and Novak Djokovic have made many more than that, and both reached the third round with routine wins today.

Spain's Nadal - a record 21-time men's singles Grand Slam champion and the winner in Paris 13 times - beat Frenchman Corentin Moutet 6-3, 6-1, 6-4.

That represents Nadal's 300th Grand Slam match victory.

Serbia's Djokovic, the world number one and defending champion, overcame Alex Molcan from Slovakia 6-2, 6-3, 7-6.

The Slovenian Aljaž Bedene awaits Djokovic in round three, while Nadal will play Dutchman Botic van de Zandschulp.

Djokovic's participation is somewhat controversial as he remains unvaccinated against COVID-19 - a decision which led to him being deported from Australia earlier this year and unable to play in the Australian Open.

Zverev, meanwhile, remains under investigation by the Association of Tennis Professionals over allegations of domestic violence, which the Olympic gold medallist denies.

The participation of the man Zverev beat in the Tokyo 2020 final, Karen Khachanov, is also controversial.

Khachanov is among the cohort of Russians able to play as neutrals, without the national flag displayed, amid the ongoing war in Ukraine which has claimed many thousands of civilian lives.

Russian and Belarusian players will be banned from Wimbledon, but at Roland Garros, 21st seed Khachanov was able to see off Bolivia's Hugo Dellien in four sets and reach round three.

Only one seed, American Taylor Fritz, was eliminated in the men's singles today.

Fritz, seeded 13th, went down 3-6, 6-2, 6-2, 6-3 versus Spanish qualifier Bernabé Zapata Miralles.