Britain's Emma Raducanu is through to the last 16 of the Miami Open after opponent McCartney Kessler retired injured at the start of the second set.

Raducanu had been utterly dominant and needed just 30 minutes to take the first set 6-1.

An early break in the second set saw the 22-year-old race into a 3-0 lead, before American Kessler, 25, was forced to retire because of a back issue.

"I could tell something was up and it is hard to stay focused when your opponent is struggling," Raducanu said in her courtside interview. "I wish her a speedy recovery because she has been playing so well.

"I am happy with my focus, it is such a big part of tennis. I haven't been at this stage of a tournament for a while.

"I returned really well and put pressure on the serve, imposing myself from the first game."

Raducanu came into the tournament with five defeats from six matches since the Australian Open and last week ended her partnership with coach Vladimir Platenik after only two weeks.

"I think it's a different approach this week," she added. "I think five minutes before the match I was playing spike ball with the team. It helps me to relax.

"When I'm playing my best tennis I'm really expressing my personality. I'd say I'm a bit of a free spirit so I don't need restrictions or being told what to do.

"I think when I'm being really authentic, that's when I'm playing my best."

Raducanu will play Amanda Anisimova in the next round after the American defeated Mirra Andreeva 7-6 (7-5) 2-6 6-3.

The 17-year-old Russian has risen to sixth in the world after winning the previous two WTA 1,000 events at Indian Wells and Dubai.