The A-League champions, Adelaide United, knocked out of the cup by Queensland "minnows" Redlands United at a cold, windswept Perry Park.

It was a night the 1564 fans who braved the conditions – and made enough noise for a crowd 10 times as big – will not forget in a hurry.

Against all odds. David v Goliath. Every sporting cliché you could imagine.

The Magic of the Cup.

The FFA Cup, now in its third year, had only previously seen A-League teams knocked out by state-based clubs twice and one of those – Green Gully's win over the Central Coast Mariners – came just on Tuesday night.

The upset result means Redlands joins fellow National Premier Leagues Queensland club – and former National Soccer League champions – Brisbane Strikers in the round of 16.

A goal down with literally seconds to spare, Redlands attacker Michael Lee capitalised on a goalkeeping howler by occasional Socceroo Eugene Galekovic to walk the ball into an open net.

Cue delirium.

Lee said the travelling Redlands supporters, 24 kilometres away from their normal home, helped inspire the team towards their epic victory.

"I loved the crowd more than anything," he said.

"As soon as we heard everyone singing 'Redlands' and everything, I felt like I'd turned into the Hulk.

"I'd never heard an atmosphere like that."

A somewhat dusty-sounding Lee, not-so fresh from a night of celebrating, said he only had one thing on his mind as he headed for goal: "Don't miss."

"I was waiting for someone to come through the back of me and bring me down," he said.

"I couldn't believe how much time I had."

​That was topped about eight minutes into extra time, when electrician Paul O'Brien sparked a frenzy of celebration as he slotted home the winner.

The day after the biggest night of his coaching life, Redlands coach Matt Chandler said he was not as surprised as most about the result.

"I felt we had a chance, to be honest," he said.

"The boys' attitude has been amazing. We worked this week on how we were going to approach the game and it came to fruition."

While Wednesday night's result made Redlands United a household name among Australian sports fans, Chandler said it had ramifications beyond the Cleveland-based club.

"It really puts Redlands on the map," he said.

"What was so fantastic last night was that there were so many of our footballing family and community in the stand watching at Strikers and I allowed a lot of the juniors and youth teams into the change rooms before and after for the team talks, just to experience that.

"I think the NPL's improved so much as well and that's why you're getting teams now in the NPL challenging the A-League teams in the cup games' one-off occasions."

Among those in the crowd at the Brisbane Strikers' home ground of Perry Park – the venue of Wednesday's match due to a lack of floodlights at the Cleveland Showgrounds – was former Socceroo John Kosmina.

Kosmina, the coach of fellow NPL Queensland side Brisbane City, dismissed Redlands' chances in the Adelaide Advertiser ahead of the match.

Chandler said he was looking forward to seeing Kosmina when their sides meet at Spencer Park on August 13.

"He was very helpful in his motivation," he said.

"But his assessment was probably right – that was the expectation and that's what makes what we've done even better."

Results such as Wednesday's stunning Redlands victory over the powerhouse of Australian football are what cup football is all about.

A competition where even pub teams, such as Darwin's Shamrock Rovers, can dare to dream of cup glory.

Chandler said football fans could expect to see more of the same as NPL teams continued to improve.

"The NPL has really helped the game in this country," he said.

"Everyone's risen the bar because we've had to, in what we've had to achieve.

"It's not that the A-League's got any worse, it's just that the NPL competition has risen the bar for football as a genuine second-tier competition."

As for the next round, Chandler said no team gave Redlands pause for concern.

"It's pretty hard to be worried about anyone, isn't it really?" he said.

"The way it was last night, maybe as much as I'd love a trip for the players, I think a home tie again, if we can get that type of support because I thought it was fantastic last night, that would give us a huge advantage.

"So someone at home – anyone at home – would be good and I'd love another A-League side."

Despite the round of 32 losses of Far North Queensland Heat and Surfers Paradise Apollo, Redlands United will not be the sole Queensland side in the FFA Cup round of 16.

The Strikers advanced with the biggest win of the 2016 FFA Cup round of 32 so far last week, with a 6-0 victory over Shamrock Rovers Darwin in the Northern Territory.

Queensland's sole A-League side, Brisbane Roar, will play Perth Glory next Wednesday night on the final round of 32 match day at Ballymore.