UPDATE 1-Olympics-Soccer-Ten-man Belgium upset Italy in thriller

(Adds coaches' quotes)

By Andrew Cawthorne

BEIJING, Aug 16 (Reuters) - Italy lost their famous defensive cool on Saturday to let 10-man Belgium score three times and squeeze past them in a quarter-final at the Workers' Stadium.

Moussa Dembele was Belgium's hero with a fine late strike clinching a 3-2 victory after his controversial first-half header was deemed over the line despite Luca Cigarina's attempted block.

Italian coach Pierluigi Casiraghi refused to blame that.

"I didn't see it. This is not an important matter," he told reporters, chiding his team for "relaxing". He added: "Three goals is not only a problem of defence, it is the midfield too."

Belgium will meet the winner of the Nigeria v Ivory Coast quarter-final, which kicked-off later.

To the delight of a rowdy 51,000 crowd, the game swung back-and-forth before 21-year-old Dembele, who plays for AZ Alkmaar in the Netherlands, dribbled free and struck with a low shot from the edge of the area on the 80th minute.

As expected, Italy had come out strongest in search of an Olympics men's soccer semi-final berth and the Belgians looked in for a tough night as defender Thomas Vermaelen was sent off for dragging down Giuseppe Rossi in the box.