Lech Poznań and Jagiellonia Białystok secured home victories while Górnik Zabrze and GKS Katowice suffered defeats.
Lech edged Faroese champions KÍ Klaksvík 1-0 to take a narrow advantage into next week's return leg, while Jagiellonia beat Scotland's Rangers 2-1.
Górnik Zabrze lost 0-1 to Hungary's Ferencváros, and Raków Częstochowa were held to a goalless draw at home by Sweden's Hammarby in the Conference League qualifiers.
GKS Katowice face an uphill task after a 0-2 defeat to Israel's Hapoel Tel Aviv.
If Lech advance, they are likely to face Switzerland's FC Thun in the Europa League playoff round after the Swiss side defeated Iceland's Víkingur Reykjavík 3-0 in their first-leg tie.
If Lech are eliminated by Klaksvík, they will drop into the Conference League playoffs.
Should Jagiellonia eliminate Rangers, they are expected to meet either Northern Ireland's Larne or Georgia's Iberia 1999 Tbilisi for a place in the Europa League league phase.
A defeat in Glasgow would send the Polish side into the Conference League playoffs, where Czech club FK Jablonec are the likely opponents after beating Latvia's RFS 2-0.
Górnik would face Turkey's Trabzonspor in the Europa League playoff round if they overturn their deficit against Ferencváros.
If eliminated, they would instead enter the Conference League playoffs against France's AS Monaco.
Raków must win away to Hammarby in Stockholm to progress.
If they do, they are likely to meet Croatia's Hajduk Split, who took a commanding 5-2 first-leg lead over Lithuania's Žalgiris Vilnius.
If GKS Katowice can overturn their two-goal deficit against Hapoel Tel Aviv, they will face Italy's Atalanta in the Conference League playoff round for a place in the competition's league phase, Polish state news agency PAP reported.
(gs)
Source: IAR, PAP