Roger Federer put on an unconvincing display en route to booking a semi-final berth at the Swiss Indoors Basel courtesy of a three-set win over Gilles Simon.

The Swiss great, who had to recover from a slow start to beat Jan-Lennard Struff a day earlier, stretched his winning streak at his home-town tournament to 18 with a 7-6 (7-1) 4-6 6-4 triumph.

But Federer was broken five times and finished with 60 unforced errors in a disjointed showing, leaving Simon to rue what might have been.

Indeed, the Frenchman raced into a 3-0 first-set lead, breaking in game two with a majestic cross-court backhand and the set appeared his when he saved three break points for a 5-2 lead.

Simon's nerve deserted him when serving for the set, though, as he sent a forehand long and Federer, having saved set point with an ace in game 12, went on to dominate the breaker.

There were four consecutive breaks of serve during an erratic second set, but a big forehand winner earned Simon a crucial third break and a 5-4 lead that he did not relinquish.

Federer surged into a 3-0 lead in the decider, only to for Simon to once again show his battling qualities to break back in game seven.

But, when serving to stay in the match, Simon went long on match point to leaving Federer breathing a sigh of relief.