The national team were able to cancel out Perparim Hetemaj's strike with Martin Paterson's penalty in the 83rd minute to salvage a draw.
O'Neill felt his team deserved a share of the spoils but was disappointed to see them let slip up an initial 2-0 lead.
"We started well with two good goals and I was obviously disappointed to lose that lead," O'Neill told reporters.
"In the second half we had to dig in and despite being careless at times we created opportunities and deserved to get the equaliser.
"I'm pleased with the performance and the young players I introduced near the end did very well."
Even though Northern Ireland are still due their first win under O'Neill's management, the friendly was a good opportunity to test prospective international players before their World Cup qualifiers, which start on 7 September against Russia.
The 43-year expanded on his praise for the younger members of the squad who made cameo appearances during the game.
"Oliver Norwood came on with about 10 minutes left and looked very accomplished in possession and played some good forward passes," O'Neill added.
"Josh Carson also came on and played well - he has quality and enthusiasm. We will see what happens regarding the Russia game but all the younger players are in contention."