This was the second of two friendlies for Lions as part of preparations for next month’s ASEAN Championship and the 2027 Asian Cup, where China will also feature.
Lee’s men beat Mongolia 4-0 on Sunday and they started the game looking assured in possession.
But it was their opponents who looked much more clinical and they almost took the lead in the 13th minute, only for Wei Shihao’s header to rebound off the post.
Minutes later, they got their reward as the Brazilian-born naturalised midfielder Sai powered a header past a stranded Izwan Mahbud.
Singapore’s first clear-cut chance came in the 21 minutes as a brilliant switch from Shah Shahiran started a flowing move, but Ryhan Stewart skied over.
And the Lions came even closer about ten minutes later as a China defender headed past his onrushing keeper Li Hao with Shawal Anuar pressing hard.
However, Li recovered well to grab the ball on the line with the nippy attacker pressing.