Serena Williams of the U.S. (right) shakes hands with Timea Bacsinszky of Switzerland after winning their semi-final match at the French Open. Photograph: Pascal Rossignol/Reuters An ailing Serena Williams stayed on course for a 20th grand slam singles title as she came back from the brink to reach the final of the French Open with a 4-6, 6-3, 6-0 win against Swiss power hitter Timea Bacsinszky on Thursday. It was for the fourth time in the tournament that Serena recovered from a set, and a break, down to win the match. The American, who looked unwell throughout the match, putting iced towels around her neck and against her forehead at changeovers, fell a set and a break down as the 23rd-seeded Bacsinszky peppered the court with backhand winners.But Williams, who won Roland Garros in 2002 and 2013, dug deep to break back and Bacsinszky cracked, losing 10 games in a row. Williams closed it out when Bacsinszky sent a backhand long and the world number one will now face Czech 13th seed Lucie Safarova on Saturday. “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…