US Open: Khachanov Reaches Third Grand Slam Semifinal After Blockx Retires in Third Set

Twenty minutes before the match ended, I closed my notebook. The result had been settled long before, but the reason I closed it had nothing to do with the score.

Louis Armstrong Stadium, Wednesday night. Karen Khachanov served in the fifth game of the third set, leading 3-2 after winning the first two sets 6-2, 7-5. Alexander Blockx, the No. 28 seed, stood at the baseline with tape wrapped around his left thigh since the second set. He called for the trainer. Staff ran out, examined his lower leg, then his back. More tape was applied. Khachanov stood at the service line, bouncing the ball, eyes on the court. For those eleven minutes, he did not once turn his head toward the other side of the net.

I wrote in my notebook: 3-2, third set, match clock at 1 hour 47 minutes. Blockx stood up, shook hands at the net, retired.

To read this match correctly, it has to be placed in its proper frame.

Khachanov arrived at this US Open unseeded. For a player who once sat inside the top ten, that is the mark of two broken seasons — minor injuries, early third-round exits, and a problem few people mention: he was losing too many points in tie-breaks. A 2026 US Open semifinal and a 2026 Australian Open semifinal had shown he could go deep on hard courts, but between those milestones and today lies a long gap American media barely bothered to fill.

On the other side of the net, Blockx was the opposite story. The 21-year-old Belgian, seeded 28th, reached the quarterfinals with an energetic game: a kicking serve, an early move to the net, and a cross-court forehand that can open the court quickly. He belongs to the type of player Grand Slams are producing in ever greater numbers: fit, relentlessly aggressive, but without a Plan B when the body stops cooperating.

There is one detail in this section of the draw few noticed. Khachanov's semifinal on Friday will come against the winner between top seed Alexander Zverev and Botic Van De Zandschulp. In the other half, No. 8 seed Ben Shelton meets No. 11 seed Frances Tiafoe — an all-American semifinal, the kind this country's broadcasters have waited a decade for. Which means every camera is pointed at the other half. This half has only a 30-year-old with no seeding, and a thigh wrap that was unwound in the locker room.

The first set ended 6-2 in 34 minutes, and the score does not capture the full extent of the control. In my notebook I recorded Khachanov's first-serve percentage in that set at 74%. More important than the number is the location: most of his first serves went up the middle, straight into Blockx's left hip. It is not a pretty serve. It cancels an opponent's rotation before the forehand can form. Blockx won 8 of 9 points on his first serve, but only 4 of 17 on his second.

The real gap in this match was not in Blockx's leg. It was in the left-hand second-serve box.

Returning second serves, Khachanov stood roughly half a metre deeper than his usual position, then stepped inside the court after the first ball to drive it cross-court. He was not trying to end points with a winner. He pulled Blockx out of position, then hit the next ball into the space that had just opened. Those are the kind of points that never make a highlight reel, and they are what made the first set so lopsided.

The second set was the decisive one, even though it ended only 7-5. On Tuesday afternoon I stood at Practice Court 7 and watched Khachanov hit for 40 minutes. Nobody else was there except two hitting partners and a coach. He repeated one drill over and over: return the second serve, step in, drive cross-court, then go down the line. There are no spectators at a practice court, but every answer is there — and on Wednesday night it appeared in the eleventh game.

At 5-5, Blockx served. The 30-30 point lasted 14 strokes, the longest rally of the match. Khachanov returned the second serve into the middle, drove cross-court into Blockx's backhand three times in a row, then changed direction down the line. Blockx got a racquet on it, but the ball found the net. Break. Khachanov served out the next game, closing the second set 7-5.

That was the turning point. Not the trainer's call in the third set.

The physical signs had come earlier. From the seventh game of the second set, Blockx's first-serve speed dropped from around 205 km/h to below 190 km/h. The number of times he broke his footwork rhythm rose noticeably in the back half of the second set. In the third set, Blockx used the drop shot three times, when he had used it only twice in the entire tournament before — the signature of a player trying to shorten points to cut down on movement. In the third set, Khachanov broke once in the fourth game and held to 3-2. The forty-page notebook never lies.

I know exactly how the coverage will be written over the next 24 hours. "Khachanov reaches the semifinal because his opponent retired." "The US Open loses a story." Some will say Blockx quit too early, that he is young and should have played it out.

Both readings are wrong at the same point.

First, the injury explains the manner of the ending, not the result. The first set and most of the second had moved in a single direction. Khachanov broke in the eleventh game of the second set, before Blockx received any medical attention at all. Had the match gone two more sets, the most plausible script was still a contest in which Blockx had to attack more with a leg that was not good enough.

Second, the phrase "unseeded" is being misread. People take it to mean "lucky." For Khachanov it means "a ranking that slid because of injuries." He is the kind of player the news cycle dislikes: no noise, no declarations, no long celebrations. The quiet sacrifice of this quarterfinal round.

And there is one more detail worth noting. A 21-year-old with tape on his left thigh, treated further on his calf and his back, after 1 hour 47 minutes in the first Grand Slam quarterfinal of his career. He did not quit. He stopped before an injury turned one quarterfinal into a lost season. Fans are entitled to be disappointed. But put yourself in the place of a 21-year-old whose back and calf are both failing, and his choice was the only one left.

What I will be watching on Friday is not whether Khachanov "takes advantage of the opportunity." It is whether he can repeat that second-serve return pattern against an opponent of an entirely different caliber. If Zverev advances, the semifinal will turn on one very specific tactical question: Khachanov hits flat, low, cross-court into Zverev's backhand — the shot the German typically uses to start a rally. Whoever has to change direction first loses the rhythm.

Three days after an afternoon on Practice Court 7, I still keep that piece of paper recording 40 minutes. Matches like this do not end on the final game. They end in practices nobody watches, and in an eleventh game that no one in the stands remembers precisely.