French Open champion Ashleigh Barty moved to within two wins of becoming world number one after seeing off Venus Williams 6-4, 6-3 to reach the semifinals of the Birmingham Classic.

Barty will edge ahead of Naomi Osaka at the top of the rankings before Wimbledon by taking the title and she extended her winning streak to 10 matches against the five-time Wimbledon champion.

Williams made the better start as the 39-year-old took a 4-1 first-set lead.

Barty, though, is also at ease on the grass and responded in style by romping through the next five games to take the set.

"I feel like every match is getting a little bit better and better on the grass, and it's just nice to give myself another opportunity to get on the grass courts and to play another singles match," said Barty.

"It's always a privilege to play against a champion like Venus.

"She's done incredible things for our sport. She's inspired generations to pick up a tennis racquet. Any time you get to play against her, it's a real privilege."

Meanwhile, the Australian admitted Friday that her decision to reluctantly rebuff Andy Murray's offer to play mixed doubles at Wimbledon was "the hardest decision" she has ever had to make.

Murray revealed on Thursday that Barty was one of the players he had approached about playing mixed at Wimbledon but she rejected the opportunity as she is already playing singles and women's doubles with Belarusian Victoria Azarenka at the All England Club next month.

"When Andy texted me asking me to play, I was a little bit shocked," she said.

"Obviously I would have loved to have grabbed the opportunity to play with Andy, and I think it was the hardest decision I have ever had to make as to whether I'm playing an event or not.

"I took some time to think about it, and playing three events is just a little bit too much. I was very flattered but said to him, 'I think there are some pretty good options out there for you.' I'm sure he'll find someone."