Tampines Rovers suffered a huge setback in their pursuit of the 2016 S.League title, after a shock 2-1 defeat to Hougang United at the Jurong West Stadium on Wednesday night.
The Stags would have leapfrogged Albirex Niigata (S) to go top with a win but were outplayed by a determined Hougang side.
Jordan Webb had cancelled Stipe Plazibat's opener and the Stags looked good to collect a point, but Japanese playmaker Fumiya Kogure popped up with a winner deep into injury time to steal all three points for the visitors.
Buoyed by a stunning comeback victory against Home United the last time out, Hougang started off the better side with M. Anumanthan lashing just wide from range on eight minutes.
The Cheetahs continued to have the upper hand and went on to take a shock lead in the 22nd minute.
A defensive lapse by Tampines left-back Irwan Shah allowed Jozef Kaplan to sneak in behind him, before the latter squared across the six-yard box for Plazibat to tap home beyond the reach of an onrushing Izwan Mahbud.
Tampines recovered well after the setback, with Yasir Hanapi testing Hougang custodian Ridhuan Barudin well from 25 yards out, before Fazrul Nawaz headed just wide from Webb's teasing right-wing cross.
The Stags duly levelled matters on the stroke of half-time as Webb rose the highest in the area to nod home Izzdin Shafiq's free kick.
Akbar Nawas' side tried to pick up where they left off after the restart, but were continually frustrated by the stout Hougang backline.
The visitors were content to hit on the counter, with one such move almost paying off on 62 minutes.
Plazibat surged forward after Izzdin lost possession and teed up Iqbal, whose shot was deflected onto the post by Jufri Taha. The loose ball fell to Kogure, who tried to wriggle free but was blocked off by Afiq Yunos.
Tampines then had the ball in the net four minutes later when Webb flicked on for Afiq to head in from close range, but the former was penalised for climbing over his marker.
The five-time champions then suffered a huge blow with striker Fazrul Nawaz coming off due to injury with 11 minutes to go and that handed the initiative to Hougang.
The Cheetahs retook the lead two minutes into injury time, with Kogure striding onto Iqbal Hussain's long ball before firing low past the stranded Izwan for the match-winner.
To rub salt to the wound, Tampines forward Billy Mehmet was sent off after the final whistle as the Stags stay one point behind leaders Albirex.
Meanwhile Hougang went two places up, to third, after the crucial win.
Tampines Rovers: Izwan Mahbud (GK), Jufri Taha, Fahrudin Mustafic (C), Afiq Yunos, Irwan Shah (Shakir Hamzah 46'), Jordan Webb, Yasir Hanapi, Izzdin Shafiq, Hafiz Sujad, Fazrul Nawaz (Sufian Anuar 79'), Billy Mehmet
Hougang United: Ridhuan Barudin (GK), Nazrul Nazari, Delwinder Singh, Raihan Rahman, Huzaifah Aziz, M. Anumanthan, Afiq Noor (Nurhilmi Jasni 88'), Jozef Kaplan (C), Fumiya Kogure, Stipe Plazibat, Iqbal Hussain