Lemmen outsprinted Italy's Christian Scaroni to win the stage, which finished atop the Orlinek climb in the southwestern resort town of Karpacz.
France's Axel Laurance finished third, 14 seconds behind the winner.
The 30-year-old Dutchman took the yellow jersey, moving six seconds ahead of Scaroni in the overall standings.
Germany's Marco Brenner is third, 26 seconds off the lead.
Poland's Michał Kwiatkowski, a former world champion, finished 24th on the stage, 21 seconds behind Lemmen, and moved into 14th place overall, 33 seconds adrift of the leader.
Twenty-one-year-old Polish rider Filip Gruszczyński, competing for the national team, impressed with a 28th-place finish, 30 seconds behind Lemmen, state news agency PAP reported.
The remaining Polish riders lost significant time, it said.
After three sprint stages, Thursday's mountainous route dramatically reshuffled the overall standings.
The 176-kilometre stage was raced in extreme heat before rain made the roads slippery later in the day.
Around 40 km from the finish, a crash involving more than 20 riders occurred near the front of the main pack.
Among those caught in the incident was Portugal's João Almeida, the 2021 Tour de Pologne champion.
According to unofficial reports, no riders suffered serious injuries.
Race officials halted the stage before restarting it after a lengthy interruption. The remaining route was shortened by about 15 km, with organizers preserving the existing time gap between a breakaway group and the main pack.
After the restart, Almeida was unable to rejoin the main field, the PAP news agency reported.
Italy's Jonathan Milan, winner of the first three stages, finished 100th, more than 10 minutes behind Lemmen.
The 83rd annual Tour de Pologne began on Monday in the northern port city of Gdynia and ends on Sunday with a 12.4-kilometre individual time trial in the southern town of Wieliczka.
The seven-stage race takes riders from Poland's Baltic coast to the Tatra Mountains, with the overall winner likely to be decided in the final time trial.
American Brandon McNulty won last year's Tour de Pologne after taking victory in the concluding time trial in Wieliczka.
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Source: IAR, PAP, TVP Sport
Click on the audio player above for a report by Piotr Urbaniak