The electrician who sparked greatest FFA Cup upset

Redlands United's Paul O'Brien revealed he had "a million things" on his mind as he prepared to score the goal that would eliminate the Hyundai A-League champions from the Westfield FFA Cup on Wednesday night in Brisbane.

O'Brien completed the PS4 NPL QLD side's incredible 2-1 extra-time win over Adelaide United on Wednesday night, converting from Tyler Bradley-Combe's pass in the 98th minute to secure a berth in the FFA Cup Round of 16.

The 27-year-old electrician picked out the bottom corner of Eugene Galekovic's goal and gave a hint of the kind of pressure he was under at Perry Park in the Queensland capital.

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"I had a million things going through my head there at the end but luckily, just slotted it to the side [of Galekovic] there, and yeah, just an unbelievable feeling," O'Brien told Fox Sports after the match.

Redlands became just the third lower-league club to overcome an A-League side in the FFA Cup's short history, joining Adelaide City and Green Gully on the list of giant-killers.

While Gully had defeated last season's A-League wooden-spooners Central Coast Mariners on Tuesday, Redlands took on the Australian champions and won.

What made the NPL Queensland club's achievement even more amazing was the fact that they entered their FFA Cup tie with just two wins from their past seven league matches.

Redlands players and officials singing the team song on the pitch after the win over Adelaide United.

Redlands captain Michael McGowan admitted no-one "really gave us a chance" and paid tribute for the way his team came from behind after Ryan Kitto had given Adelaide the lead in the 62nd minute.

"It's absolutely massive from all the boys," McGowan said.

"This is one of those things that a lot of guys will never get a chance to do again in their career. So it's one of those things they've just got to enjoy the moment."

Redlands left their equaliser until the final minute of regulation when Michael Lee took advantage of a blunder from Galekovic to stroke the ball home.

The goal saw the entire Redlands side run to Lee.

"I can't believe what happened there," McGowan said.

"When it went in and as I was running up I was thinking 'we've got another half an hour'."

What followed was arguably the biggest upset in FFA Cup history, as O'Brien scored and Redlands held on to send Adelaide home empty handed.