Underestimate cycling coach Tim Decker and his team pursuiters at your peril.
Great Britain were left rueing the error after their Australian arch-rivals spectacularly won the men's gold medal at the Saint-Quentin-en-Yvelines velodrome outside Paris.
It was a spectacular exorcism of the demons from the Tokyo Games. Alex Porter's horrific face plant when his handlebars snapped off cruelled Australia's hopes and they had to settle for bronze.
By definition, Australia's record haul of 18 gold medals meant there were underdogs among them who brilliantly exceeded expectations.
No-one put on the cape better than the pursuiters in track cycling.
They had not won a medal in the event at the world championships since Tokyo and most thought they were a podium chance, at best.
Instead Sam Welsford, Kelland O'Brien, Conor Leahy and Oliver Bleddyn qualified fastest, broke the world record, narrowly beat the British in a pulsating final and collected Australia's first Olympic gold in the event since 2004.
"I genuinely feel we underestimated what the Aussies would bring to the party. They have lifted it a huge amount and that cannot be denied - that's seriously impressive," British rider Dan Bigham said.
Decker's broad grin only dropped when, after the gold medal ride, he was asked if the Australians had surprised themselves.
"No. Never," he replied, with emphasis.
But Matt Ebden and John Peers were gobsmacked by what they did in Paris.
The unseeded 36-year-old men's doubles veterans are the second Australian tennis gold medallists after Todd Woodbridge and Mark Woodforde won the same event in 1996.
Between them, Peers and Ebden have won a hatful of titles, including grand slams. But they'd never had a moment quite like this.
"Winning slams, winning Wimbledon, we've been into the Davis Cup finals the last couple of years .... but I mean, the Olympics? Gold? Really?," Ebden said.
"Some miracle work has happened and somehow we've now got a gold medal."
They did it the hard way, too, coming from a set and 4-2 down to beat the United States in the gold medal game.
Then there's the Fox family in canoe and kayak slalom. You may have heard of them.
Big sister Jessica was one of the Australian flag bearers and then won two gold medals. But she did not make it through the kayak cross, a new Olympic event.
Up stepped little sister Noemie, who beat her older sibling in a heat and then won the final in her Games debut.
That puts the Foxes 28th on the Olympic medal tally as of late on day 15.
"You don't really dare to dream this big, but I really did this time," the younger Fox Olympic gold medallist said.
While Grace Brown wasn't quite so big a surprise when she won Australia's first gold medal, she still hadn't won a road time trial world title or an Olympic medal before her supreme performance on sodden Paris streets.
While several other favourites crashed, Brown - "little old me" - did not and she dominated.
Not all great Australian underdog stories involved gold.
Meg Harris, a hearing-impaired swimmer who waits for a visual clue when her opponents jump from the blocks, stunned herself by winning silver in the women's 50m freestyle.
Natalya Diehm broke through for bronze in BMX freestyle after five reconstructions on the same knee and several near-misses at major events.
Caitlin Parker is the first Australian woman to win a boxing medal. She and Charlie Senior won bronze, the best Olympic boxing result for Australia in 64 years.
The Australian women's water polo team upset the mighty American team on the way to silver.
And the water polo men went on a European giant-slaying run, beating Serbia, France and Hungary, before a shootoot quarter-final loss to the US.
