A host of clubs were in action on Wednesday night as they bid to book their place in the group stages of European football's elite competition, Austria Vienna among the winners
The Swiss champions ran out 4-2 victors at Ludogorets, Murat Yakin's men going in front in Bulgaria after just 12 minutes through Egyptian forward Mohamed Salah, before Marcelinho drew the home side level shortly after.
Midfielder Ivan Stoyanov then gave the hosts the lead after the interval but Basel responded in style with Salah's second of the game, a strike from Giovanni Sio and a late Fabian Schaar penalty putting them firmly in charge of the tie.
Schalke have endured a nightmare start to the new Bundesliga campaign and their chances of reaching the group stages of the Champions League are in the balance after they were held to a 1-1 home draw by PAOK.
The German side dominated the vast majority of the match at the Veltins Arena and Jefferson Farfan put them in front midway through the first half. However, Miroslav Stoch grabbed an equaliser and an all-important away goal for the Greek visitors 17 minutes from time.
Elsewhere on Wednesday, Austria Vienna put themselves in the driving seat for qualification by nicking a 2-0 win away at Dinamo Zagreb.
The Austrian champions soaked up pressure from Dinamo throughout the game and got their noses in front on 68 minutes through Marin Leovac, before striker Marko Stankovic sealed the victory seven minutes later.
Meanwhile, the tie between Steaua Bucharest and Legia Warsaw remains too close to call after the two sides played out a 1-1 draw in the Romanian capital.
Federico Piovaccari put the home side ahead with a smart finish in the first half but Jakub Kosecki grabbed a crucial away goal for the visitors eight minutes after the break.