A 25-year-old from Jiangsu was found dead in front of his computer while watching Chile play Australia in a World Cup match early on Saturday morning.
It is already the second death linked to the World Cup on the mainland. On the same day, a 51-year-old from Dalian died of a heart attack while watching the Netherlands beat Spain.
There is a time difference of 12 hours between Hong Kong and much of Brazil. So mainland and local soccer fans have to put up with sleepless nights trying to catch games that kick off after midnight.
But a lack of sleep can be dangerous. Medical experts are advising football fans to go to bed early and wake up for the games, rather than staying up all night.
Heart specialist Dr Ho Hung-kwong warned that the adrenaline rush from watching the game, combined with the lack of sleep, can raise the chances of having a heart attack. "Fans should pay more attention to their health," he said. "Eat more fruit and try to get some sleep rather than staying up all night to watch the games."
Sharon Lee, a Form Six student from St Paul's Convent School, said her secret weapon for staying awake was to wear a frozen eye patch.
"I find it useful to stay awake," she said. "I tend to fall asleep before the matches start, so I set an alarm clock. If I am still too sleepy, I will record it and watch later."