Bundesliga side Schalke kept their nerve to edge past PAOK Salonika 3-2 in Greece for a 4-3 aggregate win.
Adam Szalai's first-half opener set the Germans on their way and despite a 53rd-minute leveller from Stefanos Athanasiadis they regained control through Julian Draxler's 67th-minute strike.
A 79th-minute effort from Kostas Katsouranis gave Salonika hope but Szalai's second in the final minute sealed victory for the visitors.
Austria Vienna survived a gallant fightback from Dinamo Zagreb to squeeze through to the group stages at the Franz Horr Stadium.
Leading 2-0 from the first leg in Croatia, the hosts extended their lead in the fourth minute through a Josip Simunovic own goal.
But Marcelo Brozovic and Sammir dragged Zagreb back into it before half-time and a 71st-minute strike from substitute Fatos Beciraj drew them level on aggregate.
Vienna substitute Roman Kienast made a dramatic intervention to seal his side's place in the next stage, scoring their second just one minute after coming on as an 81st-minute substitute, as a 3-2 defeat on the night gave the hosts a 4-3 aggregate win.
Steaua Bucharest blew an early two-goal lead in Poland but clung on for a 2-2 draw on the night which gave them victory over Legia Warsaw on the away goals rule.
Nicolae Stanciu and Federico Piovaccari gave the Romanians a 2-0 lead inside the first 10 minutes before Miroslav Radovic pulled one back. Jakub Rzezniczak's injury-time effort was too late for the hosts.
Basle completed a 6-2 aggregate win over Bulgarian side Ludogorets with a 2-0 second-leg win in Switzerland. Fabian Frei opened the scoring in the 11th minute and Philipp Degen added the second 11 minutes from time.