It flashes in the blink of an eye, so fast you can barely see it, but for Brisbane's fighting schoolteacher Jeff Horn, it opens a window to a whole new world.

As he scrutinises the YouTube footage every day, while pounding the treadmill on his run towards his world welterweight title fight with Manny Pacquiao at Suncorp Stadium on July 2, the window of opportunity burns into Horn's brain.

It's near the end of Round Six of the 2012 grudge fight at the MGM Grand Casino in Las Vegas, between old rivals Pacquiao and Mexican veteran Juan Manuel Marquez.

The Mexican has been on the canvas and his nose is busted. Pacquiao smells blood, as his army of supporters urge him on.

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The Filipino terrier sways slightly from side to side, as he always does, before launching the missiles from both hands.

He nails Marquez with a booming southpaw straight left and sensing a finish, storms forward, hands down. He stabs at the Mexican with a right jab and as he prepares to launch a big, booming left follow-up, Marquez is a fraction quicker on the draw.

The Mexican's right to the chin sends Pacquiao's head bouncing back and he falls, unconscious, face first to the canvas.

Juan Manuel Marquez knocks down Manny Pacquiao in the third round during their welterweight bout at the MGM Grand Garden Arena. Photo/Getty Images
Juan Manuel Marquez knocks down Manny Pacquiao in the third round during their welterweight bout at the MGM Grand Garden Arena. Photo/Getty Images

He stays there for the next few minutes, as his wife and handlers wail over him.

It was the most stunning defeat of Pacquiao's career and one Horn believes he can replicate in what shapes as the biggest fight ever in Australia.

Promoters are hoping to lure 55,000 fans to Suncorp, far eclipsing the biggest boxing crowd ever seen in Australia - 38,000, when Azumah Nelson beat Jeff Fenech at Princes Park in Melbourne in 1992.

Fenech, a long-time Horn fan, says he is urging all Australians to get behind the Brisbane teacher and make the bout one of the great sports events of 2017.

Horn says he's not afraid by Pacquiao's whirlwind attack that has resulted in 59 wins from 67 fights and earned the Filipino boxer-turned-senator $US500 million from the sport since 1995.

"Every time he throws a punch, it gives me an opportunity," Horn said. "Every time he attacks, there's the chance for me to punch through the opening.

"Marquez stopped Pacquiao with a big shot and I've got a very good right hand, but I'm not just planning my strategy around landing one good right hand.

"I watched Pacquiao's last fight with Jessie Vargas. I'll move a lot more than Vargas did and give Pacquiao different angles, the same way he did against Vargas.

"I'm hoping to catch him off balance every time he lunges in."

Horn's trainer, Glenn Rushton, who has coached the boxer since he was a bullied schoolboy, unsure of how to throw a punch properly, says despite Horn's comparative inexperience - 17 pro fights to Pacquiao's 67 - it's time for a changing of the guard.

"It's going to be a thrilling fight, because they are both aggressive fighters who come forward," Rushton said. "They are both busy, with high workrates and both are unpredictable.

"Our plan involves a lot more than winging right hands, and Jeff is the right fighter to carry out the plan and to adapt no matter what. To me, Jeff is a younger, bigger, fresher, stronger version of Pacquiao - he will be hunting Pacquiao in every round.

"Jeff can change the angles, change the tempo and rhythm of a fight. He breaks up the rhythm of his opponent.

"Pacquiao has been knocked out and Jeff is a very heavy puncher. I think Pacquiao will really get a shock."

AUSTRALIA'S TOP 10 BIGGEST BOXING CROWDS

38,000 - Jeff Fenech v Azumah Nelson, Princes Park, Melbourne, March 1, 1992
32,500 - Jimmy Carruthers v Pappy Gault, Sydney Sports Ground, November 13, 1953
31,000 - Rocky Gattellari v Salvatore Burruni, Sydney Showgrounds, December 2, 1965
30,000 - Anthony Mundine v Danny Green I, Aussie Stadium, Sydney, May 17, 2006
30,000 - Jack Carroll v Izzy Jannazzo, Sydney Sports Ground, December 21, 1937
30,000 - Jack Carroll v Jimmy Leto, Sydney Sports Ground, January 18, 1938
27,860 - Anthony Mundine v Danny Green II, Adelaide Oval, February 3, 2017
25,000 - Jack Carroll v Bep van Klaveren, Sydney Sports Ground, December 26, 1935
23,000 - Kostya Tszyu v Jesse James Leija, Telstra Superdome, Melbourne, January 19, 2003
20,400* - Jack Johnson v Tommy Burns, Sydney Stadium, 26 December 1908
*An estimated 50,000 people waited outside the Johnson-Burns fight, unable to get tickets