Poland left Bayern Munich's Robert Lewandowski on the bench in the first half, along with Fiorentina's on-loan winger Jakub Blaszczykowski, who scored the winning goal in Wednesday's friendly against Serbia.
The game, however, was effectively over as a contest by halftime as Poland scored three goals before the break.
Stade Rennais' Grosicki opened the scoring in Wroclaw in the 18th minute, netting from a precise cross by Legia Warsaw's right back Artur Jedrzejczyk.
Two minutes later Grosicki crossed from the left for Verona's on-loan midfielder Wszolek to chip in for 2-0.
Wszolek then found Filip Starzynski, who curled the ball into the net from the edge of the area in the 32nd minute.
Wszolek scored again in the 66th minute following a fortunate rebound off a Finnish defender after being set up by Grosicki, who completed the rout with five minutes remaining having collected a 40-metre pass from defender Bartosz Salamon.
Poland beat Serbia in a friendly on Wednesday, having beaten Iceland and the Czech Republic in friendlies last year and ended their Euro 2016 qualifying campaign with a win over Ireland.
Poland are in Group C at Euro 2016 along with world champions Germany, Ukraine and Northern Ireland.
(Reporting by Adrian Krajewski; Additional reporting by Marcin Goettig; Editing by Toby Davis)
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