The hosts continued their winless run despite taking the lead against the defending champions, who added three more points to their advantage at the top
The win lifted the leaders eight points clear of nearest challengers Albirex Niigata (S) and 10 ahead of third-placed Tanjong Pagar United going into the international break; they still have one game in hand.
When the competition resumes in 15 days’ time, Tampines and Albirex will meet at Clementi Stadium, where the Stags will be keen to turn the screws even tighter.
Here, they fell behind after 14 minutes to a breakaway goal crafted by Sahil Suhaimi inside his own half, who picked out a lurking Afiq Noor on the halfway line.
The Tampines defence was caught square just inside their own half as Afiq sprinted to the edge of the penalty area. He then angled the ball across the face of goal for the arriving Iqbal Hussain on the left to slot home.
But after some tactical adjustments by coach Tay Peng Kee, the Stags managed to claw their way back with an expertly taken freekick from Kunihiro Yamashita powerfully driven from the edge of the penalty area and into the roof of Syazwan Buhari’s net.
That was after 34 minutes and a couple of minutes later, Shahdan Sulaiman put Tampines in the lead for the first time. Aleksandar Duric cut the ball back from the left for his team-mate to slot home from close range, with Khairul Amri the man setting Duric free.
Just when it looked as if the Young Lions might find something extra, Tampines scored again, this time from the penalty spot.
Firdaus Kasman had hit the post and the ball was cleared for a corner in the 61st minute. The corner came over and Duric nodded the ball on for Yamashita, whose header was saved by the keeper only for a second header to be stopped on the line by the hand of Young Lions player Farhan Rahmat.
The offender was sent off for his trouble, with Mustafic Fahrudin dispatching the penalty with his usual clinical precision two minutes later.
A second penalty after Jamil Ali had been brought down seven minutes later saw skipper Fahrudin score again from the spot and while Syazwan guessed the right way, the ball was struck too firmly for him to reach it.
A Yamashita own goal in the 75th minute after Sherif El Masri’s shot from the left had been spilled by goalkeeper Ridhuan Barudin made it 4-2 but that was scant consolation for the luckless Young Lions, anchored as they are and totally adrift at the foot of the competition ladder.