Naomi Osaka hits back at critics after thrilling comeback win in Stuttgart

World No 1 beats Donna Vekic 6-3, 4-6, 7-6 before issuing denial she has been struggling this year

Japan's Naomi Osaka serves to Croatia's Donna Vekic during their Porsche tennis Grand Prix match in Stuttgart on Friday. Marijan Murat / AP Photo

World No 1 Naomi Osaka has hit back at her critics after fighting to a dramatic comeback win over Donna Vekic to reach her first career clay court semi-final in Stuttgart on Friday.

The 21-year-old Japanese battled back from 1-5 down in the final set to beat Vekic 6-3, 4-6, 7-6 but denied that she was struggling this year.

"I don't know why people are saying I am having a bad season," she said. "I won the Australian Open, right?"

Despite securing her second grand slam title in Melbourne, Osaka had not reached a semi-final since then before her thrilling fightback in Stuttgart, having suffered early exits in Dubai, Indian Wells and Miami.

She conceded that the defeats, and the pressure of being No 1, had affected her.

"I would be lying if I said it didn't bother me. You can tell because I get antsy on court, whereas before, if I made a mistake, I would just act on it.

"When I am at my best, I wake up wanting a new challenge. In this phase, I felt like I was waking up just wanting to win."

Osaka said that she had tried to "think logically" when she found herself on the brink of defeat in Friday's quarter-final.

"I try not panic anymore, because that costs energy," she said. "I just told myself I didn't want to come away from here with any regrets."

In Saturday's semi-final, Osaka will face Estonian eighth seed Anett Kontaveit, who reached the last four after former world No 1 Victoria Azarenka retired hurt in the final set of Friday's rollercoaster late match.

Azarenka was serving for the match in the second set, but eventually threw in the towel after struggling with a shoulder complaint at 0-3 down in the decider. "It's going to be a very tough match tomorrow," Kontaveit said of her semi-final clash with Osaka.

Osaka cannot lose her number one spot in Stuttgart, but she will be looking to keep a healthy points lead over world number three Petra Kvitova, who also won her quarter-final.

Kvitova overcame a rocky start to beat Latvia's Anastasija Sevastova 2-6, 6-2, 6-3.

"It was really difficult today, but I am very happy to be in the semi-final. I feel good and healthy," Kvitova said.

In the semi-final, the Czech will face Dutch sixth seed Kiki Bertens, who beat home favourite and reigning Wimbledon champion Angelique Kerber 6-3, 6-4.

"It's going to be a tough match. Petra is a great player, so I am looking forward to it," Bertens said.