Roger Federer has not hit top form all week in Basel and he needed more than two-and-a-half hours to hold off the troublesome French veteran.
The 33-year-old Frenchman did not disappoint his home crowd as he beat the Croatian in three sets 1-6, 6-3, 6-2 to reach the final of the tournament.
Roger Federer's freak knee accident - reportedly as he played with his children last Saturday in a Melbourne park following his semi-final loss to Novak Djokovic - has caused major repercussions at the Rotterdam World Tennis tournament, which usually draws at least one world-class headliner.
Novak Djokovic battled for four hours, 32 minutes at the Rod Laver Arena before beating Gilles Simon 6-3, 6-7 (1/7), 6-4, 4-6, 6-3 and will now play Japan's Kei Nishikori in the Australian Open last eight.
Gilles Simon suffered knee and ankle injuries after taking nasty falls in his 4-6, 7-6 (7/5), 6-3, 6-0 defeat against Andy Murray.
Gilles Simon, the world number 11, took just less than two hours to demolish James Ward on the grass-courts of Queen's Club in west London.
Roger Federer will be playing his 37th Grand Slam semifinal on Friday.
Thanasi Kokkinakis lost 6-4, 6-2 to French seventh seed Gilles Simon. The Aussie later said that he was distracted during the match.
Fifth seed Gilles Simon beat seventh seed Gael Monfils 6-4, 1-6, 7-6 to win the Marseille Open title for the second time.
The Australian Open finalists suffered an upset at the hands of Frenchman Gilles Simon who won 6-4, 6-2 to reach semis of Rotterdam World Tennis event.
World Number 20 Gilles Simon now heads to Melbourne Park for final practice prior to the Monday start of the Australian Open.
Jo-Wilfried Tsonga, Gael Monfils, Richard Gasquet, Julien Benneteau and Gilles Simon had been recalled after helping France beat the Czech Republic 4-1 in the semi-finals in September.
Roger Federer will return to number two on the back of his run in Shanghai but he said getting back to number one, a position he last held two years ago, had not entered his thinking.
Roger Federer registered a 6-4, 6-4 win over world number one Novak Djokovic to dent his hopes of clinching a third successive title.
Gilles Simon defeated Feliciano Lopez of Spain 6-2, 7-6 to reach his first Masters-level final in six years.
Gilles Simon, 29, is yet to win a Masters title but he is in a rich vein of form and previously overpowered Australian Open champion Stan Wawrinka on Wednesday in Shanghai.
Gilles Simon of France went down in five sets against Croatia's Marin Cilic on Tuesday in a fourth round tie of the US Open.
While five-time Grand Slam champion Maria Sharapova was defeated by Danish 10th seed Caroline Wozniacki, Gilles Simon sent Spanish fourth seed David Ferrer crashing to his earliest US Open defeat in five years.