PARIS — Four days ago, Jakub Mensik was slumped in a wheelchair on the red dirt of Roland Garros, his body shutting down from heat and cramping after a second-round win in sweltering conditions. On a cool Thursday evening, rain-freshened air hanging over Court Philippe-Chatrier, he stood at the net having just saved seven match points and beaten fellow teenager João Fonseca in four sets. The optics were almost too good to be true. They were also entirely real.

Mensik's path through the bottom half of the draw has required something beyond tennis. Against Fonseca — the Brazilian prodigy who entered the fortnight as one of the tournament's most electric stories — he absorbed a ferocious challenge and refused to flinch. Down and staring at elimination on multiple occasions, Mensik saved all seven of those match points and closed out the victory in what he described afterward as "a really insane level" of tennis over the final stretch. That is not the language of spin; it matches what the scoreboard and the match statistics bore out.

The historical weight of the result is not trivial. Mensik, still 20 years old, has now surpassed what Ivan Lendl — the dominant Czech force in men's tennis for a decade — achieved at Roland Garros at the same stage of his career. That comparison will make Czech tennis federations quietly ecstatic and will put pressure on a young man who, to his credit, has not yet shown much sign of wilting under it. His serve held up. His forehand was explosive when it needed to be. And crucially, his nerve was something Fonseca, for all his gifts, could not match on the day.

The match points saved are the number that will follow Mensik into his semi-final preparation. Seven is not a rounding error; it is a portrait of a player who spent significant portions of the match on the brink of elimination and chose, each time, not to go over. That mental dimension — the thing that separates the players who make Grand Slam semis from the ones who lose in the quarters in tight four-setters — is what the result confirmed about Mensik that his ranking and results until now had only hinted at.

His reward is a semi-final against Alexander Zverev, the world number two and the heaviest favorite remaining in the draw. Zverev is a Roland Garros finalist, a player who has matured significantly on clay in the past two seasons, and a physical problem for anyone across the net. The consensus framing — that Mensik is the feel-good underdog — is accurate but incomplete. Mensik holds a Grand Slam title already, has beaten top-ten players on big stages, and will not be intimidated by the occasion. Whether he can solve Zverev's serve-and-forehand combination on a clay surface is a different question, and an open one.

Meanwhile, the women's draw has its own teenager making noise, and she is doing it with far less drama. Mirra Andreeva, the 17-year-old Russian, dispatched Romanian veteran Sorana Cirstea 6-0, 6-3 in a performance that was less a tennis match than a demonstration. Cirstea is no soft draw — she has made major quarter-finals and beaten seeded players at Slams — but Andreeva moved through her with the kind of clean, pressurized ball-striking that has characterized her entire fortnight. The scoreline was not a fluke.

Andreeva reached the semi-finals at Roland Garros last year as well, making her the rare teenager who treats the French Open's late rounds as familiar territory rather than novelty. She will face Ukrainian Marta Kostyuk, a player whose tour record this year reflects someone peaking at the right moment and whose opponent in the quarters she also dispatched with clinical efficiency. The Andreeva-Kostyuk semi-final sets up as a genuine contest between two players who have been the best women at this tournament, and it deserves more attention than the men's draw has been absorbing.

For Mensik, the hours before Friday's semi-final carry their own subplot. At his post-match press conference, he was visibly dealing with cramping again — a reminder that the physical toll of his run is real and accumulating. Whether his body cooperates across five sets against Zverev is not a narrative device; it is a legitimate variable. What is not in question is that a 20-year-old who was in a wheelchair earlier this week has positioned himself one match from a Grand Slam final. On the evidence of what he has done to get there, writing him off would be a mistake.