Paris - American tennis great Billie Jean King said on Wednesday she thinks Johanna Konta is playing "the best" she has in her career so far.
The 28-year-old Konta became the first British woman since 1983 to reach the French Open semi-finals with an impressive straight-sets win over last year's runner-up Sloane Stephens on Tuesday, and will face Czech teenager Marketa Vondrousova for a final place on Thursday.
It will be Konta's third Grand Slam semi-final, after the 2016 Australian Open and Wimbledon two years ago.
"Konta right now is probably playing the best I've ever seen her play. I think she's actually better now," said 12-time major champion King on Wednesday at an International Tennis Federation press conference in Paris.
"She's really concentrating well and she's hitting so big. Her serve is big, her groundstrokes are big. She's totally focused right now. She just has to stay the way she is.
"I think her concentration is better now, day in, day out. I think sometimes she just gets a little hyped up too much and she seems to be very calm right now."
Konta, who had never won a French Open main-draw match before this tournament, is looking to become Britain's first women's Grand Slam champion since Virginia Wade won Wimbledon in 1977.
Only three of the top-10 women's seeds made the quarter-finals at Roland Garros this year, with Konta putting out seventh seed Stephens, while third-seeded defending champion Simona Halep and eighth seed Ashleigh Barty are yet to play against Americans Amanda Anisimova and Madison Keys respectively.
King believes the unpredictability of the tournament is good for the women's game, after both world number one Naomi Osaka and 23-time Grand Slam title winner Serena Williams both crashed out in the third round.
"I think anyone can win in women's tennis right now. We don't have like the old days with Chris (Evert) and Martina (Navratilova) -- that top two or three, like the men do right now," said King.
"That makes it for me personally that much more interesting, because it's such a toss-up."