Karolina Muchova apologised to the crowd after taking several trips to the toilet during her US Open quarter-final.

The world No. 52 beat Beatriz Haddad Maia 6-1 6-4 in an unusual match which saw both players call the doctor and physio to the court.

Muchova repeatedly ran off the court despite having a comfortable lead in the match.

The Czech star still managed to get the job done in straight sets, booking her spot in a second consecutive US Open semi-final. And she apologised to the fans during her on-court interview.

Asked what was going on physically, Muchova replied: "Little weird match I have to say. I had a little problems I wouldn’t like to comment on it actually if it’s fine. But I’m happy manage it with some run to the bathroom and back."

Laughing, she added: "Sorry if it disturbed anyone but I had no other choice!"

Muchova also reached the semi-final last year, losing to eventual champion Coco Gauff. But she didn't play another match for 10 months after a wrist injury threatened to derail her career. After undergoing surgery, the 28-year-old returned to the tour in June.

After beating Haddad Maia, the former world No. 8 admitted that she didn't expect to make it back into the semis so soon. "Yeah I’m really happy. Wouldn’t say that before the tournament," she confessed.

Muchova will now face either Iga Swiatek or Jessica Pegula. Looking ahead, she said: "Every round is very tough here and I’m sure it’s going to be a tough and exciting match."