Jason Donohue’s side led 1-0 at the break but were undone by the concession of two goals early in the second half.
Poland had an early chance when Michal Rakoczy fired narrowly wide in the third minute but Ireland grabbed the lead in the 10th minute when Conor Carty found the net with a looping header from a Ronan McKinley corner.
Irish keeper Enda Minogue did brilliantly to deny Kamil Duskiewicz two minutes later after the Polish attacker was sent through on goal.
Poland drew level in the 45th minute when Filip Szymczak fired home from the penalty spot after Seamus Keogh was penalised for a challenge in the Irish box.
Szymczak put the home side ahead in the 52nd minute when he header to the net following a Polish corner. Troy Parrott rattled the woodwork midway through the second half.
Ireland’s best chance to level came with two minutes left when a free-kick by McKinley was pushed wide by the keeper and the Irish failed to capitalise on the resulting corner.
Irish head coach Jason Donohue paid tribute to the work his players and staff had put in for these two friendly games, which are the first for the this group of players on the international stage.
“There was a controversial penalty then scored from a set-piece but outside of that we dominated. We had our game plan, went ahead, they hit couldn’t break us down then a poor six minutes cost us," he said.
“We were really happy with the players. They showed great improvement from Tuesday and were very confident in possession. They showed no nerves and had Poland on the back foot for the majority of the game. The Polish coach was very complimentary about our performance afterwards.
“Unfortunately Jack Funge didn't quite recover from his injury but we've got the chance to see 17 of the 18 in the games this week so that's very positive. There'll be more opportunities in the future.
“I really want to give a big thank you to all the staff. The work that has been put in was tremendous in our first game together, the players had a really good experience and the staff were very strong part of it."
REPUBLIC OF IRELAND: Enda Minogue, James Furlong, Brandon Holt, Cormac Moore, Troy Parrott, Sean McGrath, Josh Girugi, Timi Sobowaile, Conor Carty, Ronan McKinley, Seamus Keogh. Subs: Ademipo Odubeko for Carty 48 mins; Sean Kennedy for McGrath 48; Alex Dunne for Holt 62; Festy Ebosele for Girugi 72.