Serena Williams survives Bacsinszky scare to reach final

An out of sorts Serena Williams overcame illness and the plucky spirit of Swiss underdog Timea Bacsinszky to clinch a place in the French Open final.

The world number one came back from a set down for the fourth time at this tournament to triumph 4-6 6-3 6-0 and set up a showdown with 13th seed Lucie Safarova.

"I have tried everything. I thought if I lose I must fight. I have tried and tried, I don't know where I found the energy," Williams told a courtside interviewer in French before a coughing fit ended the conversation.

"I have been feeling unwell for a few days," she later added in a statement, explaining she had to see the tournament doctor after the match.

Williams had been spotted looking unwell in the lead up to the clash and after a bright start she was broken by some exquisite returning in the fifth game.

Last year, Williams pulled out of a doubles match with her sister Venus at Wimbledon after appearing disoriented and weak on court when she was suffering from a viral illness. There was no quitting this time, however.

Number 23 seed, Bacsinszky had never gone beyond the third round of a Grand Slam until this event in Paris, but showed no signs of being overawed as she rattled the winners past a clearly uncomfortable Williams.

Both players showed fine spirit and resilience but it was Bacsinszky who was gifted the opener on a third set point when Williams let a possible break back slip.

The American looked in real trouble when she was broken to trail 3-2 in the second set, but roared back to take the next four games and tee up a decider.

Williams, who was still looking unwell between points, ran away with it in the third as she stretched her winning streak to 10 games to complete the bagel and stay on course for a third French Open crown.