It took a second after he tapped the wall. But as soon as he realized it, Jon Sieben threw his arms up and fell backwards into the water. At the 1984 Los Angeles Olympics, Sieben had pulled off one of the greatest swimming upsets in Olympic history.

At the 150-meter mark in the men’s 200-meter butterfly , Sieben didn’t even deserve a mention, behind the favorites. In fact, Sieben’s name doesn’t get mentioned until about 25 meters to go when the American announcers, including Mark Spitz, realize that Sieben in lane 6 has pulled even with the mighty Michael Gross.

• Spitz: Gross, look out!
• Play-by-play Announcer: Here comes Vidal! Here comes Siemen in lane six! This is going to be a horse race! Sieben is about to pull a huge upset! In lane 6, 17-year old Jon Sieben of Queensland Australia, came on in the last 20 meters and he caught michael Gross and beat him to the wall!

Gross had already set two world records in swimming at those 1984 Los Angeles Olympics, and was gunning for a third. The massive 2 meter tall Gross from Frankfurt West Germany, nicknamed “The Albatross”, expected to fend off other favorites Pablo Morales of the US and Rafael Vidal of Venezuela, but did not expect to be challenged by the 176 cm tall Sieben from Brisbane, Australia, affectionately nicknamed “The Shrimp”.

As David Wallechinsky and Jaime Loucky write in The Book of Olympic Lists, Sieben was so overwhelmed with his victory, he didn’t realize he had set a world record as well.

His time of 1:57:04 was more than four seconds faster than his pre-Olympic best of 2:01:17. Sieben was so excited by his victory that it was not until an hour later that he realized that he had broken the world record. The rabidly pro-US crowd gave him a standing ovation, and the outcome was so delightful that the defeated favorites expressed pleasure more than disappointment. Gross, who had refused to appear before reporters following his two gold-medal races, and whose disdain for pomp and press had earned him the nickname “The American” in West Germany, sat beside Sieben after the 200 butterfly preferring to praise the young Australian rather than talk about himself.

Watch the video below to see this stunning upset. Note that the announcer’s throw-away lines about Sieben in the introduction turned out to be true: “Third in the commonwealth games in 1982…a bit of an outsider….but you don’t count out any Australian from medal contention in these Games.”