Two-time champion Porto won 1-0 in Lille, and Celtic took advantage of a reprieve from UEFA to play in the competition by drawing 1-1 at Maribor.
Russian league leader Zenit St. Petersburg's 1-0 victory at Standard Liege helped ensure all five home teams failed to win.
APOEL is favoured to advance next week in Cyprus after drawing 1-1 against Aalborg in Denmark.
BATE Borisov took a 1-1 draw back to Belarus after Slovan Bratislava got an 80th-minute equalizer from veteran Slovakia forward Robert Vittek.
Second-leg matches are played next Tuesday, two days before the 32-team group stage is drawn in Monaco. Each club is then guaranteed at last 8.6 million euros ($11.5 million) in prize money from UEFA.
Porto and Lille both finished third in their national leagues last season, and it was Portugal which looked the classier act on this evidence.
The only goal, in the 61st minute, had a World Cup flavour to it.
Porto's Mexico midfielder Hector Herrera pounced from close-range after Lille's Nigeria goalkeeper Vincent Enyeama parried a header by Jackson Martinez, the Colombia forward.
Lille rarely threatened, though defender Sebastien Corchia shot over from eight meters (yards) in the 45th after his first shot was blocked.
Celtic, the 1967 champion, owed its appearance in the playoffs to UEFA's lawyers after losing home and away to previous opponent Legia Warsaw. Celtic advanced when the Polish champion was punished for fielding a suspended player.
The Scottish side led in the sixth minute from a third goal in the competition by Callum McGregor, who seized on a loose ball after Jo Inge Berget's shot was saved.
Maribor, seeking a first group-stage appearance for 15 years, levelled eight minutes with Damjan Bohar's goal.
Celtic would have retaken the lead but Stefan Johansen, standing on the goalline, inadvertently blocked teammate Virgil van Dijk's header.
After four straight wins in its national league, coach Andre Villas-Boas' Zenit team also won in Belgium.
Brazil forward Hulk's pass across the penalty box set up Oleg Shatov's winning goal in the 16th minute.
APOEL, a surprise quarterfinalist three seasons ago, made its first shot on target count in the 54th minute at Aalborg. Brazilian midfielder Vinicius finished a surging run into the penalty area with a rising shot into the net.
The Danish champion Aalborg had dominated the first half and took the lead with Nicolaj Thomsen's shot in the 16th from 15 metres (yards).
BATE are well set to reach the group stage for the fourth time since 2008. It led with a 44th-minute own goal by Slovan defender Tomas Jablonsky.
Vittek, whose four goals at the 2010 World Cup included two to eliminate defending champion Italy, came off the bench late to level the match with a left-foot shot from a tight angle.