Top seed and defending champion Grigor Dimitrov moved into the semi-finals of the season-opening Brisbane International after seeing off a brave challenge from an injured Kyle Edmund on Friday.

Dimitrov was on court for almost two-and-a-half hours before finally subduing the British number two, who was right in the contest until he hurt his ankle with the score at 4-4 in the third set.

Edmund was wrong-footed on the baseline and collapsed to the ground with a scream of pain after turning his ankle.

While the crowd held their breath, fearing the 22-year-old Englishman had done some major damage, Dimitrov hurdled the net and ran to his opponent, eventually helping him hobble off court.

But after having his ankle strapped the Englishman was able to carry on, although his movement appeared restricted.

Dimitrov held his serve to go to 5-4 and then broke Edmund to seal the win 6-3, 6-7 (3/7), 6-4.

"At the end of the day, health above all," Dimitrov said immediately afterwards.

"It's very unfortunate what happened, for sure. I've seen this too many times, I know the feeling. I really hope he gets better."

"I knew the last two games he wasn't at his best so I just had to find a way again," Dimitrov added.

Edmund's injury comes days after British men's number one Andy Murray pulled out of the Australian Open due to his ongoing hip injury and women's number one Johanna Konta retired in her Brisbane quarter-final, also with a hip problem.

Dimitrov will now play mercurial Australian Nick Kyrgios in a blockbuster semi-final.

Earlier in the day Kyrgios came back from losing the first set to defeat former finalist Alexandr Dolgopolov 1-6, 6-3, 6-4.

The Australian number one admitted he was flat at the start of the match before switching on at the start of the second set.

"Obviously, today, I started pretty poorly -- no energy in the first set -- but I always knew that I was going to come through," he said.

"I played some pretty good tennis in the second and third sets. That's just me, I guess. Very unpredictable. I don't really know how I'm going to come out.

"As bad as it is to say, it's kind of like a tap. I can turn it on when I want to and turn it off."

The second semi-final will be between Australian wildcard Alex de Minaur and American Ryan Harrison.

The 18-year-old de Minaur stunned fourth seed Milos Raonic in the second round and there was no letdown Friday as he ousted US qualifier Michael Mmoh 6-4, 6-0 to reach his first ATP semi-final.

Harrison moved through when his opponent, Uzbekistan's Denis Istomin, retired due to a left hip injury with the American leading 7-6 (8/6), 4-2.

Source: AFP