MELBOURNE, Australia — Coco Gauff's retooled forehand and serve abandoned her in the worst way and at the worst time at the Australian Open. The unforced errors just kept accumulating Tuesday, and so did the double-faults and break points, often followed by a palm placed over her eyes or a slap to a thigh.

Add it all up, and Gauff's trip to Melbourne Park — and her 13-match winning streak that dated to late last season — ended in the quarterfinals. Never able to take control on a hot afternoon in Rod Laver Arena, the 2023 US Open champion was eliminated by No 11 Paula Badosa of Spain 7-5, 6-4.

Using tweaks to some key strokes, and a change to her coaching team after a disappointing end to her title defense in New York in September, the 20-year-old Gauff arrived in Australia with hopes of earning a second Grand Slam title.

"I feel like (at the) US Open, I was playing with no solution, so that was more the frustrating part. Today, I feel like I'm playing with solutions; I know what I need to work on. US Open, I needed to work on my serve. Not saying that my serve is where I want it to be, but I worked on it; obviously, a big improvement. So I want to continue working on that, continue working on playing aggressive," Gauff said.

"So I feel like I'm on the road to the right way, right path," she said. "Even though I lost today, I feel like I'm in an upward trajectory."

The American entered Tuesday with a 9-0 record in 2025; she also won her last four matches of last season to collect the trophy at the WTA Finals in November.

"Just a lot more work to do," Gauff said after the 1-hour, 43-minute loss to Badosa, who had been 0-2 in Grand Slam quarterfinals. "I'm obviously disappointed, but I'm not completely crushed."

Badosa now heads to her first Grand Slam semifinal at age 27 — and less than a year after she was contemplating retirement because of a stress fracture in her back that took what felt like forever to heal and did not initially respond to cortisone injections.

"I wanted to (give) it a last try," Badosa said, "Well, here I am. So I'm really proud of what we went through with all my team and especially how I (fought) through all that, especially mentally."

She was hurt during a practice at the tournament in Rome in May 2023, shortly after she began working with coach Pol Toledo. A year later, including several months off the tour, there still were issues.

"The reality is that the back was not responding. We couldn't find a solution. Paula was frustrated," Toledo said. "I was like: This is not working. I don't know what we have to do."

Relying on a new doctor, fitness coach and nutritionist, Badosa tried different exercises and supplements, and her back improved.

"The puzzle," she said, "started to look better."

On Tuesday, she kept the pressure on Gauff, who finished with 41 unforced errors, including six double-faults and 28 missed forehands. Badosa compiled 10 break points and won four of Gauff's service games. Gauff, meanwhile, never earned so much as a single break point until after already down a set and a break.

One key game — and one that illustrated Gauff's problems on this afternoon — started the second set. It lasted 22 points spread over more than a dozen minutes, and Badosa converted her fifth break chance after Gauff missed two forehands in a row.

Of Badosa's 12 points in that game, 11 came via mistakes by Gauff, including seven errant forehands.

"Today," Gauff said, "she did better in those key moments."

When Badosa ended the quarterfinal with a forehand winner, she placed her hand over her mouth, then knelt on the ground and bowed her head. This was a big moment for someone who reached a career-best ranking of No 2 in 2022, but only now believes she's reached her full potential.

"Emotionally, I wanted it so much," Badosa said. "I'm never going to feel freedom until I win the tournament. I'm always like this. It's my personality. It's my character."

Zverev raises his game

Alexander Zverev played his best tennis when it mattered most to down Tommy Paul 7-6 (1), 7-6 (0),2-6, 6-1 on Tuesday and reach his third Australian Open semifinal in five years, keeping alive his dream of finally landing a Grand Slam title.

The 27-year-old German was unable to find his peak level for much of a match played in the stifling afternoon heat at Rod Laver Arena but dominated his American opponent in tiebreaks to lock up the first two sets.

Paul bagged the third set but second seed Zverev upped his intensity to whip through the fourth.

"To be honest, I should have been down two sets to love, he played better than me. I was not playing great," Zverev said after reaching his ninth Grand Slam semifinal, the most among active players who have not won a major.

" (Somehow) I'm up two sets to love and all of a sudden, I need only one more set, and the fourth set was definitely the best that I've played.

"I'm obviously extremely happy to be back in the semifinals."

Paul, also 27, had beaten Zverev in their two previous meetings and worked assiduously to gain the upper hand in the first two sets only for the German to raise his game to drag him back into a dog fight.

The 2023 semifinalist converted his fourth break point to take a 6-5 lead in the opening set but Zverev returned the favor in the next game before racing away with the tiebreak 7-1.

Agencies