Khachanov Survives Tien in Five as US Open Fourth Round Reshapes Both Draws

The fourth round in New York delivered the tournament's first genuine test of endurance. Karen Khachanov needed five sets and every ounce of his baseline discipline to see off Learner Tien 7-5 4-6 6-7 6-1 6-4, recovering from a two-sets-to-one deficit against an opponent who had dragged him into the kind of extended rallies that usually favour the younger man. The turnaround was decisive rather than gradual: Khachanov won the fourth set 6-1 and then held his nerve through a tight decider.

If that was the marathon, Botic Van De Zandschulp produced the escape act. The Dutchman lost the first two sets to Arthur Gea before rescuing the match 3-6 6-7 7-6 7-6 6-4, winning back-to-back tie-breaks to level and then closing out a fifth set that his opponent will replay for some time. Two tie-breaks in the middle of a five-setter is the sort of sequence that decides fortnights, and it has put Van De Zandschulp deep into the second week again.

The day's most eye-catching name, though, was Alexander Blockx. The Belgian took out Francisco Cerundolo 6-3 4-6 7-5 7-5, converting two consecutive 7-5 sets against an established top-level opponent — a scoreline pattern that speaks to composure at the business end of sets rather than to any single flash of shot-making.

On the women's side, the two headline acts were emphatic. Coco Gauff beat Iva Jovic 6-1 6-4, controlling the first set almost entirely before absorbing a spell of resistance in the second. Elena Rybakina was equally clinical against Naomi Osaka, winning 6-1 6-4 in a matchup of two of the biggest first-strike games in the sport. The identical scorelines tell the story of a round in which the favourites, once they found their range, did not linger.

Away from Flushing Meadows, the Challenger circuit produced its usual quota of three-set attrition. In Barranquilla, Varvara Lepchenko came through a tight opening set to beat Katrina Scott 7-6 6-1, Kayla Day handled Suzan Lamens 6-4 6-3, and Anastasia Tikhonova outlasted Darja Semenistaja 6-4 4-6 7-5. On the clay of Montreux, Tessa Johanna Brockmann recovered from a set down to eliminate Tamara Zidansek 4-6 7-6 6-3, while in Antalya, Leyre Romero Gormaz needed three sets and a final-set tie-break to edge Berfu Cengiz 6-7 7-5 7-6, arguably the most gruelling result of the day anywhere.

The schedule now sharpens. The quarterfinal of the day belongs to Aryna Sabalenka, the world number one, against Linda Noskova, ranked sixth. Sabalenka's hard-court authority is the tournament's constant reference point; Noskova's flat, early-struck ball is one of the few in the draw capable of taking time away from her. It is a stylistic collision more than a mismatch of levels, and the margin will sit in the first four shots of each rally.

The men's quarterfinal pairs Frances Tiafoe, ranked 12th, with Alex Michelsen, ranked 46th, in an all-American meeting that guarantees a home semifinalist. Tiafoe carries the New York pedigree and the crowd; Michelsen arrives as the lower-ranked man with the cleaner recent path and nothing structurally to lose.