Britain's Katie Boulter is through to the Miami Open third round after teenage opponent Brenda Fruhvirtova was forced to pull out through illness.

Boulter, who is Britain's leading women's player after a strong start to 2024, led 7-6 (7-5) 1-0 when 16-year-old Fruhvirtova decided to stop.

After leading by an early break, the Czech started to suffer in the Florida heat and twice asked to see a doctor.

"To win like that, I'll take it but I want her to get better," said Boulter.

Speaking to Sky Sports, she added. "Halfway through the match I'm seeing her coaches telling her to pull out and then she's not.

"One minute she's struggling to put the ball in the court and the next she's running 10 shots side to side. It's a tough mental game."

While it was not the way Boulter wanted to progress, the 27-year-old will take positives from the way she maintained focus in the difficult circumstances.

Ultimately, she will be relieved to earn her first victory at the Miami Open, which is a WTA 1000 event and one of the biggest outside the Grand Slams.

It was far from Boulter's best performance, falling short of the level which helped her win the biggest title of her career at the San Diego Open last month and climb to a career-high ranking of 27th in the world.

Fruhvirtova was a break up in the first set and playing confidently as Boulter - who lost in the Indian Wells first round just days after her San Diego triumph - was unable to find range with her aggressive shot-making.

But momentum shifted when the teenager needed to see a doctor before she was about to serve for the set at 5-4.

Boulter tried to up the intensity and lengthen the points, further sapping Fruhvirtova's energy levels.

Boulter broke back for 5-5 and went on to win the tie-break, then took the serve of Fruhvirtova - whose execution of her shots was increasingly erratic - again at the start of the second set.

Fruhvirtova, who is regarded as one of the most exciting talents on the WTA Tour, asked to see the doctor again before conceding the match.

"For me it was challenging and I wasn't the kindest to myself but we live and learn," added 24th seed Boulter, who received a first-round bye and plays Brazilian 11th seed Beatriz Haddad Maia in the last 32.

"There is a lot to improve on but I'll take it."