What is the most stunning sports upset ever? [View all]

I just watched on the Tennis Channel as they were replaying the 2016 Australian Open women's championship between Angelique Kerber and Serena Williams, won by Kerber 6-4, 3-6, 6-4. A couple of times the commentators mentioned the previous Grand Slam tournament, the 2015 U.S. Open, when Serena Williams was going for the calendar year Grand Slam. She had already won that year's Australian Open, French Open and Wimbledon. It's been a long time since anybody won all four Grand Slams in the same year, men or women. Serena came pretty close in 2015, though, and at the time everybody expected her to accomplish that rare feat. But first she had to deal with Roberta Vinci in one of the U.S. Open semifinals. Everybody was sure Serena would win that match; nobody, myself included, thought Roberta Vinci had any chance at all. But I watched the whole match live anyway. Serena won the first set, and then I thought, ho-hum, here we go. But big surprise, Vinci actually won the second set, forcing a third and deciding set, and then, she won that set too, eliminating Williams 2-6, 6-4, 6-4, and advancing to the final. It was, in my humble opinion, the most stunning, the most incredible sports upset I have ever seen in my 75 years on this planet. Nine years later, I still can't believe it really happened, even though I watched it on TV live with my own eyes.

What do y'all think is the biggest, the most stunning, sports upset of all time?

— Ron