Nearly No.1: Ashleigh Barty is two wins away from moving top of the rankings

French Open champion Ashleigh Barty 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 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."

Australian star Barty made the Birmingham semi-finals on Friday by beating Venus Williams 6-4, 6-3 and now stands just two wins from becoming the world number one.

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

"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."

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.

The Australian had to stave off break points in her opening service game of the second set, but then took control with two breaks of the Williams serve to set up a meeting with Barbora Strycova in Saturday's semi-finals.

Strycova got the better of an all-Czech battle to beat Kristyna Pliskova 6-2, 6-4 to reach the last four in Birmingham for the fourth time in six appearances.

In the other semi-final, German Julia Goerges takes on Petra Martic, who survived five match points to oust former French Open champion Jelena Ostapenko.

Martic trailed 5-2 in the second set having lost the first on a tie-break, but rallied to win the next five games before tearing through the third 6-1.

"I still can't believe that I won this match," said Martic.

Goerges, a Wimbledon semi-finalist in 2018, was far more comfortable in a 6-3, 6-2 victory over Yulia Putintseva who had knocked out world number one Osaka on Thursday.

Nearly No.1: Ashleigh Barty is two wins away from moving top of the rankings