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His team emerged from the halftime break at Forsyth Barr Stadium with a 12-10 lead.
Southern still had a man in the bin and Harbour had enjoyed the better of the final exchanges in the opening half.
If Harbour had struck next, the game might have ended very differently.
Instead, it was Elton's opposite who cast a little magic and ripped the game away from the Hawks in the opening moments of the second spell.
Magpies halfback and skipper Josh Walden scooped the ball up from the base of a ruck, nipped down the blindside and into a gap.
When the cover defence closed, he chipped ahead for winger MacKenzie Haugh, who got a friendly bounce and ran in for his third try.
''I think it was definitely the turning point,'' Elton said.
''We had our tails up and that kind of brought us back down. That really hurt and I don't think we ever really came back from that.''
Prop Mike Mata'afa muscled over midway through the second spell to seal a 24-15 win.
''Obviously we are gutted because we didn't come away with the result we were after.
''We didn't put in the performance we wanted to put out there either.
''Full credit to Southern. They were the team to beat all year and they showed that [on Saturday].''
The Hawks lost prop Aidan Spence in the warm-up but Southern had to change plans quickly as well, with fullback Bryce Hosie picking up an injury in the first two minutes.
Haugh replaced Hosie and really shone, scoring three tries.
But it was Southern's powerful set pieces that set up the win.
''The set pieces were always going to be Southern's strength and I think they probably dominated that again.
''Early on they blew right over the top of our scrum. Their lineout was strong too.
''We had a plan coming into the game but we probably didn't execute that as well as we had hoped to.''