O’Neill, a silver medal winner at the 2010 European Championships, progressed following a 7-4 win over Vladimir Mievskij of Lithuania and will face Turkish middleweight Adem Kibici in today’s final.
Ward, who beat 2007 world bronze medalist Daugirdas Semitas on Wednesday, followed that with a 9-7 verdict over Poland’s Wladzim Letra.
Nevin beat England’s Gamal Yafai 10-9 to book his ticket into today’s 56Kg final and Sheenan outgunned Partir Umit of Turkey 12-7.
The victory was sweet revenge for the Cavan bantamweight Nevin as he was beaten by Yafai in the quarter-finals of the European Senior Championships in Moscow last summer.
Irish team manager Des Donnelly added. “The lads got three great wins under their belts today and their confidence will be high for tomorrow’s finals. The John Joe Nevin bout with the English lad was a fantastic contest.
“John was eager to set the record straight from the European meeting and he did that. We’ll have another big day ahead of us again on Friday.”
Seventeen nations are competing in Warsaw. Billy Walsh and Zuar Antia are working Ireland’s corner at the tournament.
Meanwhile, Ken Egan is part of a seven-man Irish squad taking part in the Gee Bee Multi-Nations which begin in Helsinki today.
Semi-finals: 56Kg: JJ Nevin (Cavan) bear G Yafai (Eng) 10-9. 75Kg: D O’Neill (Paulstown) beat V Mievskij (Lithuania) 9-4. 81Kg: J Ward (Moate) beat W Letra (Poland) 9-7. 91Kg: C Sheehan (Clonmel) beat P Umit (Turkey) 12-7.