The Queensland Reds sparked up with three long-range tries in the final 20 minutes of an otherwise dour contest to win 26-17 and notch a third-straight Super Rugby Pacific triumph.
The visitors were left scratching their heads though after Triston Reilly, replacing the injured Joseph-Aukuso Suaalii in the centres, had his incredible diving effort scratched off.
The former West Tigers flyer kept his body well above ground and planted the ball in the corner despite close attention to put his side ahead 21-19 with six minutes to play.
But his effort was swiftly waved away after the Television Match Official (TMO) judged the ball to have been planted on the sideline in the in-goal area.
Replays suggested Reilly may have found clean grass with the first contact of the ball though, before it continued to roll onto its side and touch the sideline.
Gordon, who had earlier finished a brilliant Jock Campbell line-break and offload, then hopped over a tackler and raced 55 metres around Harry Potter to break NSW hearts.
Waratahs coach McKellar said his side paid for not winning those "little moments", that included the Reilly no-try call and some lapses in defence that led to the Reds' late glut of tries.
"If you speak to how they're refereeing and using the TMO, if the referee awards the try, unless it's clear and obvious, it stays a try. Is that not right?," the clearly miffed coach said.
"I'm incredibly proud of the effort we put in. Big games like this, it's little moments and that's a little moment you hope goes your way.
"But it didn't. And there were others.
"If you want to be a top-four side you have to win those moments and we didn't.
"They're the harsh learnings, and you sit here very disappointed."
Saturday's Suncorp Stadium clash was a dour affair for almost an hour, with the Waratahs unable to convert their possession into points and the Reds content to kick in behind the visitors.
Waratahs hooker Ioane Moananu found the line for a 12-7 lead after 57 minutes and it seemed to awaken the Reds.
Gordon crossed then Isaac Henry linked up with rampaging winger Filipo Daugunu, who had weaved through traffic after substitute Treyvon Pritchard's earlier line-break shook things up.
Reilly was denied and then Gordon iced the contest for the hosts.
Reds coach Les Kiss said he was relieved to see Reilly's try waved away but confident his side - who made 181 tackles to the Waratahs' 104 - had time and means to concoct another victory regardless.
"It takes a toll but we knew if we stayed in the fight … I was rapt for the boys that they took those turnover moments and just backed themselves," he said.
Gordon's bomb in the first half led to a Harry Wilson try as the Test flyhalf, who scored last week's match-winner against the ACT Brumbies, again showed his wares after a stint in the NRL.
The hosts improved to 3-1 before next Saturday's trip to Fiji, where they've never won.
The Waratahs, who thumped the Reds in the first round, dropped to 2-2 but showed far more resolve than in their 59-19 loss to the Hurricanes a week ago.
Flanker Charlie Gamble was a late out for the visitors with a tight hamstring, replaced by English product and first try-scorer Jamie Adamson.
20°C