The 22-time major champion, who first claimed the Musketeers’ Cup in 2005 and last lifted the trophy in 2022 before a serious hip injury disrupted his career, had hinted that this year might be his final one on the tour.
Having returned to the tournament that he skipped in 2023 and refusing to confirm any farewells ahead of his opener, Nadal showed flashes of top form again on Court Philippe Chatrier but the 37-year-old ultimately went down fighting.
Victory meant Zverev became only the third man to beat Nadal at Roland Garrosafter Novak Djokovic and Robin Soderling, with the German banishing memories of his retirement due to an ankle injury when the duo last met in the 2022 semi-finals.
Nadal was broken by in-form Rome champion Zverev in the opening game and surrendered his serve again late on to drop the first set in unfavourable conditions for him with the roof closed due to heavy rain.
Faced with the prospect of only his fourth Roland Garros defeat in 116 matches, Nadal made a positive start to the next set as he leapt and pumped his fists after holding for 2-2 and broke for the first time with a delicate drop.
The crowd began to sense a comeback as Nadal went ahead 4-2 with some vintage shots on both flanks but the steely Zverev hit back in the 10th game and saved two breakpoints before doubling his advantage by edging a high-octane tiebreak.
Watched on by his great rival Djokovic and a host of other current players, Nadal surged to a 2-0 lead in the third set but squandered it as Zverev drew level and dealt another body blow in the seventh game.
The boisterous crowd tried their best to roar Nadal on but Zverev held his nerve to clinch a famous victory that could well prove to be the springboard he needs to push for an elusive first Grand Slam title.
(With inputs from Reuters)
