Xaver Schlager helped Salzburg to a win in their final group stage game against a Schalke team that finished top of Group I.
The hosts had needed a goalless draw to progress to the last 32 of Europe's second-tier competition.
John Guidetti's header proved to be the game-winner as Celta defeated Panathinaikos to advance to the round of 32.
Celta Vigo claimed their place in the last 32 of the Europa League with a straightforward 2-0 win over Panathinaikos in Athens.
Flares and fireworks thrown by fans onto the pitch caused the match between Ajax and Standard Liege to be stopped temporarily.
Anwar El-Ghazi scores a stunning. first-half volley against Standard Liege as Ajax earn a 1-1 draw and top Group G.