First-half goals from Qasim Said and Eid Al Farsi sank the Lions at Jalan Besar Stadium, Singapore, and left them without a point after two games in Group A.
Stange took over the Southeast Asian champions in May as he extended a globe-trotting career which has included stints with his native East Germany and Iraq. The German pledged to instill a slicker, passing game. But despite promising signs in the second half, Singapore offered little in attack and could have lost by more.
With the visitors coping well with the artificial surface and humid conditions, Said drilled their opener across the keeper on 14 minutes to finish off an incisive move. Al Farsi doubled their lead on the stroke of half-time and after the break, Said nearly grabbed his second before the pace slowed towards the finish.
Stange brought on 17-year-old Adam Swandi in the second half but the promising attacking midfielder was unable to spark a revival. Oman move provisionally top of Group A with a maximum six points, while Singapore's next assignment is against Syria in October as they aim to reach the 2015 Asian Cup in Australia.