Turner, who rides for the Ineos Grenadiers cycling group, powered ahead in the uphill finish to beat Spain’s Pello Bilbao (Bahrain-Victorious) and Italy’s Andrea Bagioli (Lidl-Trek) to the line.
The top Polish finisher was national team rider Marcin Budziński, who came in 10th.
The stage was temporarily halted after a crash 22 kilometres from the finish line.
Six riders were involved, including race leader Paul Lapeira of France, who, despite initial reports, managed to finish the stage, Polish state news agency PAP reported.
Poland’s Rafał Majka was also affected but rejoined the main pack before the race was neutralised.
Wednesday’s route was the most grueling of the race in terms of elevation, with 3,465 metres of climbing over a relatively short 159.3-kilometre course.
In the overall standings, Lapeira retains the yellow jersey with an eight-second lead over Monaco’s Victor Langellotti and 12 seconds ahead of Switzerland’s Jan Christen.
Czech rider Mathias Vacek, who was in second place overall, did not finish the stage.
Majka is the top-placed Polish rider in the general classification, currently sitting in 10th.
Thursday’s fourth stage runs from Rybnik to Cieszyn over 201.4 kilometres in the south of the country and may offer the final opportunity for sprinters, despite a challenging climb midway through the route, organizers said.
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Source: IAR, PAP, polskieradio24.pl