Chess upsets are always entertaining, more so for the upsetter than the upsettee, but once in a while there's an upset of such magnitude that it gets attention way beyond the tournament itself. So it was in the 2000 Malaga Open when a 14-year-old girl defeated a leading grand master it made chess headlines around the world.
The grandmaster was Vladimir Epishin (2667) and the girl was Arianne Caoili (2078). Epishin played 37...Qxe4 leaving his unguarded queen up for grabs. The problem was that if Arianne snatched it he would win it back with a family fork and her position would have been in tatters.
She didn't panic. She thought, "I'll have that queen, but I'm not going to take it just yet. Let's have a check first."
So, check she did and Epishin resigned.
Play through the game--it's worth it.
Arianne was the young lady who again made world headlines six years later when she became the the centre of the Gormallygate ruckus. (I wrote a story about it at the time for our chess club web page. You can find it here: http://www.rootyhillchess.org/caoili.html)