Swiss football's defending champions and current league leaders St Gallen have suffered a 4-1 defeat at the hands of the 1999 champions, Servette Geneva.
Two early goals from midfielder Johann Lonfat and a 44th minute strike from Goran Obradovic helped Servette to a 3-1 lead at half-time, with Marco Zwyssig grabbing St Gallen's only reply.
After the break, Servette striker Alex Frei completed the convincing scoreline with his second goal for the Genevan side since moving from Lucerne at the end of the winter break.
The win lifted Servette into second place in the championship table, level on points with St Gallen. Marcel Koller's team will be toppled on Sunday though if either Lugano or Grasshoppers Zurich manage home wins.
The winter champions Lugano are due to take on Gilbert Gress' FC Zurich, while Grasshoppers are pitted against the Basel team of their former manager Christian Gross.
In Saturday's only other match, Lausanne climbed into fourth spot at the expense of bottom side Sion. Polish striker Marcin Kuzba was the Lausanne hero, giving his side a 2-0 lead with goals either side of the break.
Cameroonian defender Armand Deumi pulled Sion back into the game on the hour mark, but his goal provided nothing more than consolation in the eventual 2-1 defeat.
swissinfo with agencies