Defender Patrik Vydra scored the only goal of the match for the home team in the northern Czech city of Mladá Boleslav in the 76th minute, public broadcaster Polish Radio’s IAR news agency reported.
After five rounds of fixtures, Jagiellonia sit in eighth place in the Conference League standings, leaving their direct qualification for the knockout stages of the European competition uncertain.
They began their campaign in early October with a 2-1 away win against Danish top-flight side FC Copenhagen. This was followed by a 2-0 home victory over Moldovan team Petrocub Hîncești, and a commanding 3-0 triumph over Norway's Molde on November 7.
In its fourth group-stage match, the Polish team played out an exciting 3-3 draw with Slovenian side Celje on November 28.
Coached by Adrian Siemieniec, Jagiellonia now turn their focus to their final league-phase fixture, a home clash with Slovenian side Olimpija Ljubljana, scheduled for December 19.
Meanwhile, Polish top-flight heavyweights Legia Warsaw succumbed 1-2 to Swiss club Lugano at home in their fifth league-phase match on Thursday.
Both Polish teams have one remaining match in the group stage, which concludes on December 19.
The top eight sides in the league phase of the new-look Conference League will qualify automatically for the knockout stages, while the teams finishing in ninth to 24th place will compete in a two-legged play-off to secure a place in the last 16 of the competition.
Teams ranked 25-36 will be eliminated from the competition, run by European football governing body UEFA.
Source: IAR, PAP, polskieradio24.pl