Home United's AFC Cup campaign got off to the worst possible start after a 1-0 defeat by Group E minnows New Radiant from Maldives.
The turning point of the match - which was played in Male, Maldives - arrived in the 53rd minute when Protectors goalkeeper Shahril Jantan was sent off.
He was adjudged to be the last man when he brought down New Radiant attacker Ali Fasir in the penalty box.
Hong Kong referee Ng Kai Lam flashed Shahril the red card and New Radiant's Mohammad Umair made no mistake from the spot.
The Protectors had a chance to equalise late on when they were awarded their own penalty after a foul on Qiu Li.
The 32-year-old forward, who rejoined Home from Balestier Khalsa before the start of the season, stepped up to take the spot-kick but was denied by goalkeeper Imran Mohamed.
In the other Group E match played on Tuesday, Indonesia's Persipura Jayapura beat India's Churchill Brothers 2-0 to top the group.
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