The duo defeated Americans Mackenzie McDonald and Frances Tiafoe 7-5, 7-6 in the quarterfinals on Tuesday.
Zieliński and Nys will now face Spain's Marcel Granollers and Argentina's Horacio Zeballos for a place in the championship match at the clay-court tournament in the Italian capital.
Zieliński and Nys in January reached the final of the Australian Open men's doubles in Melbourne, where they lost 4-6, 6-7 to home favourites Rinky Hijikata and Jason Kubler.
Playing in the Grand Slam final in Australia was the biggest success for the 26-year-old Pole in his career so far.
Last year, Zieliński reached the quarterfinals of the US Open with Nys.
The Polish player has two doubles titles to his name, both earned at the Metz Open, with countryman Hubert Hurkacz in 2021 and with Nys last year.
The 2023 Italian Open runs until Sunday.
(gs)
Source: IAR, PAP