Sanchez was victorious in Sion after a 184km stage four trek from Bulle to Sion that saw 38 riders arrive at the finish together despite there being three category one and a category two climb on the stage.
Wiggins arrived at the finish with Sanchez but because the Spaniard took a 10-second time bonus with the win – he now leads on General Classification by nine seconds.
Rinaldo Nocentini (AG2R La Mondiale) finished second in the stage with Branislau Samoilau (Movistar) completing the top three.
Despite a number of splintered attacks – all the big contenders arrived together at the finish.
That means that with just one 16:5km individual time trial to go – the top 35 riders are separated by just 35 seconds.
Time trial specialist Wiggins and Michael Rodgers (16 seconds) are directly behind Sanchez, promising an exciting final day in the race.