Qatar, who looked to be in deep trouble when they trailed India 1-0 with 11 minutes left on Tuesday, ensured they finished top of Group D with a 31st minute strike from Hatim Abdelaziz and another by Ahmad Abdil deep in injury time.
"What a great spirit we showed all through the game," said Qatar captain Amaral Marcone. "It was very important that we got through to defend our gold medal. we hope that the spirit of 2006 returns for 2010. We can win the title again."
The Indians put Singapore on the back foot with 13 minutes gone when Jewel Raja Shaikh got the opener. The floodgates opened in the second half, with further goals from Jibon Singh Khangeman, Singh Balwant and Maithani Minish before the Young Lions got a late consolation. It was a poor tournament for Singapore, who are out of the running and face an early plane home.
Joining them on the scrapheap are Bangladesh who were hammered 4-1 by Hong Kong, with Au Yeung Yiu Chung grabbing two goals and Ju Ying Zhi and Chan Man Fai piling o0n the misery for the hopelessly outclassed Bangladeshis.
Mohammed Hoque briefly pulled his side level at 1-1 midway through the first half with his team's only goal of the tournament, but Bangladesh finished pointless in three matches having conceded 10 goals.
Hong Kong, who face Oman in the next stage, collected seven points from their three matches but finished runners-up to Group E winners UAE on goal difference after the Gulf side saw off Uzbekistan 3-0. Theyab Al Musabi put the UAE in front after ten minutes with Ahmed Al Jenaiby adding a brace courtesy of a strike in each half. UAE will tackle Kuwait for a place in the quarter-finals.
Hong Kong coach Wai Ching Tsang was delighted to see his side progress. "In 52-years, it's the first for us to get into the second round at the Asian Games. It shows our players can play better football," he said.
"This is the message to people in Hong Kong and beyond. I'm very satisfied with today's result. We are confident and now we hope to advance into the semi-finals and not just the quarter-finals."
His UAE opposite number Mahdi Ali Redha was equally pleased. "We develop players so they have a will to win. If you have that then anything is possible," he said.
In Group F, Bryan Robson's Thailand ensured they stayed in the tournament but gave a patchy performance in a drab 0-0 draw with minnows the Maldives. It was equally bad from Pakistan, who enlisted the help of Robson's former England colleague Graham Roberts to help them here. His influence failed to work as they crashed 2-0 to Oman, who qualify with Thailand as the Pakistanis head home.
Asian heavyweights Japan and South Korea, along with hosts China, wrap up their qualifying campaign on Saturday, a day after the Asian Games officially start.