Coco Gauff’s defence of her maiden major title collapsed in a welter of double-faults as she lost in three sets to fellow American Emma Navarro.

The result continued the unpredictable narrative of this US Open, which has already lost its two biggest male stars: Novak Djokovic and Carlos Alcaraz.

Since Serena Williams played her final match here two years ago, Gauff has become the most famous name in American tennis (among active players, at least). She delivered on her promise by winning the US Open last summer, while still only 19.

At the time, Gauff’s breakthrough looked like it might mark a turning point in her career, prefiguring an imperial phase in which she delivered multiple trophies.

A year on, it hasn’t quite worked out that way. Even if Gauff continues to be one of the WTA Tour’s most consistent performers (she and Jasmine Paolini are the only women to reach the fourth round of all four majors this season), she has only added one title to her collection, and that came in the relatively low-key season-opener in Auckland.

Gauff’s ongoing technical issues were all too obvious against Navarro: a clean and consistent hitter who had also knocked her out of Wimbledon this summer at the same stage.

Despite the work of Andre Agassi’s former coach Brad Gilbert, Gauff still regularly loses control of her two most important shots – the forehand and the serve. It’s only because she is so good in every other department – backhand, movement, net-play and mentality – that she remains a fixture in the world’s top five.

“I don’t think I’ve ever seen her play that poorly in a match,” said Chris Evert, who was providing commentary for the ABC network. The statistics were certainly damning. Gauff hit a massive 19 double-faults – almost five full games’ worth – which contributed to an equally alarming tally of 60 unforced errors.

Gauff’s famed fighting spirit helped her recover from a slow start to level the match at one set all, through sheer willpower as much as anything. But the decider found her at her most erratic. Gauff played 35 points on her own serve in the third set, and they were divided almost equally into first serves, second serves and double-faults.

After the match, Gauff insisted that she had played well off the ground, but acknowledged that “I just didn’t take care of my serve”. As she went on to explain, she has a technical weakness that involves the left side of her body snapping down too early in her action, when she would be better off standing taller and reaching up for the ball.

Asked whether she might emulate world No2 Aryna Sabalenka, who hired a biomechanist to rebuild her malfunctioning serve, Gauff said that she would consider any option at this stage.

“I definitely want to get other opinions,” she said. “I think it’s sometimes more of an emotional, mental thing because if I go out on the practice court right now, I would make, like, 30 serves in a row. I’ve done it before.

“But, yeah, I definitely want to look at other things because I don’t want to lose matches like this anymore.”

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