The Polish team won 99:84 (29:18, 17:28, 23:17, 30:21) in the Group D match at the O2 Arena in the Czech capital Prague, news outlets reported.
With their home advantage, the Czechs had appeared to be slight favourites. Yet the Poles, led by captain Mateusz Ponitka, who scored 26 points, were far superior on the day, according to przegladsportowy.onet.pl.
Poland next play Finland, also in Prague, on Saturday.
Their remaining opponents in Group D are Israel, Serbia and the Netherlands.
The best four teams will qualify for the knockout stages.
The FIBA EuroBasket 22 is being co-hosted by the Czech Republic, Georgia, Italy and Germany.
The tournament runs until September 18.
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Source: przegladsportowy.onet.pl, sport.tvp.pl, fiba.basketball