Billie Jean King believes Johanna Konta is a better player than when she reached the semi-finals of Wimbledon.

The British number one will play in the last four at a grand slam for the third time when she takes on Czech teenager Marketa Vondrousova on Friday.

Neither was expected to make it this far, but both have been in great form and, such is the unpredictability of the women's game, it would not be a big surprise if any of the six players left in the draw went on to win the title.

Konta is obviously among those, and King sees no reason she cannot end the fortnight with the trophy.

"I think anyone can win in women's tennis right now," she said. "It's such a toss-up. Every time we talk among ourselves, 'Who's going to win?', it's like, 'We don't know'. Whoever is playing well that week.

"And Konta is playing the best I've probably ever seen her play except for when she had that run at Wimbledon. But I think she's actually better now.

"I think her concentration is better day in and day out. I feel like some days she gets like too hyped up and she seems to be very calm right now.

"I can tell she's had a lot of therapy and I think it's helped her. She's quite clear now in her thoughts in what she wants to do and she just keeps improving. Because she wants to. You can tell she wants to keep improving.

"She's really concentrating well and she's hitting so big – her serve's big, her ground strokes are big. She's totally focused right now. She just has to stay on, stay the way she is."

King, who was announced on Wednesday as a global ambassador for Fed Cup, has also been impressed by 19-year-old Vondrousova, who is through to the last four at a slam for the first time.

"She's good, definitely, really interesting," said King, the French Open champion in 1972.

"You know what's back in our sport now in a huge way? It's drop shots. They went away for years. There was no variety and now it's amazing how the players have more variety. You see players going to net more now as well. This is so much more fun."

Vondrousova will pose plenty of problems for Konta if she can play at her best, but one area where the British player does have the advantage is in experience having been here before at the Australian Open in 2016 and Wimbledon two years ago.

The boot was on the other foot in her previous two semi-finals, losing to Angelique Kerber in Melbourne and Venus Williams at SW19.

"It helps she's had that experience a lot," said King. "I think she's in the best position she's ever been because she's had more experience, she's won more, she's learned more."