Young Boys missed the chance to extend their lead at the top of the table as they went down 3-1 at Sion.
Goals from Saidi Aladu Adeshina, Obinna Nwaneri and Alvaro Dominguez put the hosts three up before Matar Coly grabbed a consolation for Young Boys, who remained seven points ahead of Basle.
Basle, though, have a game in hand.
Elsewhere, Lucerne beat Zurich 1-0 thanks to a second-half goal from Kwabena Asamoa-Frimpong.
