By Gabriel Tan
The Stags looked headed for victory at the Jalan Besar Stadium after opposition goalkeeper Shahril Jantan gifted them a goal in the 25th minute when he inexplicably palmed a harmless cross by Ismadi Mukthar into his own net.
However, Shimpei Sakurada equalised in the 78th minute and the game looked headed for extra-time, only for substitute Erwan Gunawan to emphatically smash an effort home in injury-time to win the tie for the Warriors.
While the loss has ruined Tampines' hopes of winning the domestic double this year, Tay wants his men to bounce back by sewing up the league title on Friday when they take on Harimau Muda in the final match of the season.
"It's not the end of the world," he said. "We still have another one to play for.
"This [the cup final] is over now and there's nothing we can do about it. We have to look towards the next game which, in my opinion, is more important for us.
"The focus now is to psyche the boys up again after this defeat, there's so much to play for in the league title race."
The ex-Singapore international felt his side had been the better team in the first half but admitted Sakurada's equaliser turned the tie in the Warriors' favour, and also lamented on the lack of depth in his squad.
"We played well and I believe we dominated the first half," Tay added. "In the second half, we played more cautiously and unfortunately we conceded two late goals.
"The equaliser really demoralised the players.
"We have a very shallow squad and you could see that in the last 20 minutes, we had no defensive players to bring on even though we wanted to hold on to our lead."
A win against Harimau would see the Stags win their second straight league title but anything less than that would open the door for second-placed DPMM FC, who play at home to Balestier Khalsa on the same evening.