By Gabriel TanFollow @@gabetan13
Although the Stags fell behind at the Jalan Besar in the 19th minute after an unfortunate own-goal from Anaz Hadee, they went in level at the break after Sead Hadzibulic equalised nine minutes later with a well-taken header.
However, the Indian visitors stormed to a two-goal lead shortly after the hour mark thanks to goals from Andrew Barisic and Chidi Edeh, and although Khairul Amri pulled one back in the 65th minute, the Stags' hopes of a comeback were ended when Barisic netted his second three minutes from time.
The result leaves Tampines bottom of Group H with just a point from their opening three games, and they - along with Selangor - are now six points behind East Bengal and Saigon Xuan Thanh.
Nonetheless, Bacina is refusing to give up hope as long as they have a mathematical chance of progressing to the Round of 16.
"Of course it's not over," he said. "There are still three games to be played and, mathematically, we still have a good chance.
"It's never nice to concede four goals but I don't think we deserved to lose by this scoreline. They took their chances while we didn't, and we have to admit they were the better side tonight [Wednesday]."
"I told my players to stay positive and that we tried our best; now we're looking forward to the next game.
"I know that they tried their best and my job is to stay positive and spread my optimism in the dressing room. Now we have to regroup and try to upset East Bengal in Kolkata."
The Croat did however admit the manner in which they conceded the first goal was a real blow, and concedes they sorely missed suspended captain Mustafic Fahrudin and centre-back Seiji Kaneko, who has not been registered for the AFC Cup.
"They [East Bengal] played on the counterattack and really put us under pressure, especially in the second half," Bacina added.
"The first goal we conceded was very soft and it killed us a lot psychologically, but I don't want to blame the players at the back.
"In the [Great Eastern-YEO's] S.League we have conceded the least goals yet we are conceding a lot in the AFC Cup. It's clear one of the reasons for that is because Kaneko isn't playing, while we also missed Mustafic, who is a key player for us.
"But I don't want to blame the players at the back. They [East Bengal] showed they have quality with the chances they scored.
"Chidi is a good player and he's the top scorer in India; I think he's scored 90 per cent of their goals. Andrew and [Penn] Orji are also good players and they [East Bengal] are second in the I-League for a reason."
Tampines also played in the AFC Cup last season and failed to make the knockout round after finishing bottom of a group consisting of Kitchee, Terengganu and Song Lam Nghe An.
Image courtesy of WSG