Katie Boulter reached the third round of the Miami Open for the first time after opponent Brenda Fruhvirtova retired with illness.

The British number one, who received a first-round bye as the 24th seed, was leading 7-6 (5) 1-0 15-0 when 16-year-old wild card Fruhvirtova, who appeared to be struggling with the heat, headed to her chair.

The young Czech, who was short on tennis coming into the tournament having been under the weather, called the doctor for the first time leading by a break of serve at 5-4 in the opening set.

Boulter eventually took the set in a tie-break and had broken to start the second before Fruhvirtova called the doctor again and then decided she could not continue.

She is not the first player to struggle in Miami this week, with Frenchman Arthur Cazaux collapsing on court during a qualifying match, while Matteo Berrettini looked close to fainting against Andy Murray on Wednesday.

Boulter had made a shaky start and admitted she found it hard to concentrate amid her opponent’s difficulties, telling Sky Sports: “I actually think it’s one of the toughest things to do.

“Halfway through the match I’m seeing her coaches telling her to pull and then she’s not, so obviously there’s a lot going on. One minute she’s struggling to put the ball in the court and the next she’s running 10 shots side to side so it’s a tough mental game.

“For me it was challenging today and I probably wasn’t the kindest to myself but we live and learn.”

Boulter will next face 11th seed Beatriz Haddad Maia, who she beat last month on her way to the San Diego title, in the last 32.

Dan Evans defeated Italian Lorenzo Sonego for the first time in four attempts to post a much-needed win.

Things did not look promising for the 33-year-old, who had won only two of his eight matches in 2024, when Sonego raced to the first set but Evans dug in and turned the match around to claim a 1-6 6-3 6-4 victory.

The British number three had lost to Sonego in Miami last year and at the Australian Open in January, and he let out a huge roar of delight at the end.

“He was way better than me and I wasn’t really moving him,” said Evans. “I just made up my mind to start coming in and trying to dictate and see where it got me.

“I served very well, which made it a lot easier. I’m really happy. It’s been a tragic year so far. It’s only tennis, though.”

Eighth seed Maria Sakkari, runner-up to Iga Swiatek in Indian Wells last weekend, continued her good form with a 6-2 6-2 victory over Yuan Yue but Caroline Wozniacki lost out 5-7 7-5 6-4 to Ukraine’s Anhelina Kalinina.

In the first round of the men’s event, former US Open finalist Kei Nishikori, playing just his fifth tournament since 2021 and first of the season, was beaten 6-3 6-4 by Sebastian Ofner.

Murray followed up his singles victory over Berrettini on Wednesday by teaming up with American Sebastian Korda to beat Britain’s Julian Cash and Dutchman Tallon Griekspoor 7-5 6-4 in the first round of the doubles.