Northern Ireland paid the price for a nightmare first half as Romania took victory at Soldier Field in Chicago.
Tiberiu Balan put Romania ahead after seven minutes and Daniel Nicolae added a second just six minutes later.
Lawrie Sanchez's side went close through Gareth McAuley but their task was made all the harder after James Quinn's 38th-minute sending-off.
The second half saw Northern Ireland continue to attack, but they were unable to find a way through.
Romania took their early lead after Nicolae's skilful run took him into space and he cut the ball back for Balan to tuck home.
The second goal was also a straightforward affair as Romania's pace took them clear on the breakaway before the impressive Nicolae converted.
After the early setbacks, Northern Ireland pushed forward with McAuley unlucky not to score and striker Peter Thompson forcing a good save from Romania keeper Cohan Danut.
But Quinn's dismissal - for a reckless challenge - forced them onto the back foot again.
After the half-time break, McAuley and Dean Shiels both forced decent saves from Danut, while Northern Ireland keeper Alan Blayney had to keep out efforts from Ruga Mugure and Cristian Chivu.
Romania: Coman, Badoi, Goian, Maftei, Pulhac, Bostina, Nicolita, Radoi, Niculae, Balan, Ruga.
Northern Ireland: Blayney, Duff, Capaldi, Craigan, Davis, Clingan, Sproule, Quinn, McAuley, Shields, Thompson.