Adam Williamson's final conversion was the cause of some controversy
Diss have taken the lead in London League Division 2 North, with just one game of the season remaining.
The Norfolk team lead by a point after leapfrogging Staines by beating them 15-13 amid controversial circumstances.
Staines appealed against the award of a conversion, but Diss coach Gavin Brock said their complaint was pointless.
"Our touch judge put his flag up, their touch judge put his flag up, the scorecard shows it's a conversion so that's where it stays," he said.
Staines had been top of the table since before Christmas, but Diss have chased them all the way, and Brock said the whole club had pulled together at just the right time.
He told BBC Radio Norfolk: "They really pulled a hell of a game out of the bag, the whole squad, one through to 18, even the injured lads who travelled with us. It was an honest, hearty performance from all the lads.
"When the teams came out the cheer for Diss was just as large as Staines, and they stayed vocal as they have done all season."
Diss' home ground, Mackenders, is expected to be packed for their final game of the season on Saturday, 18 April against Letchworth, the only team to have beaten Diss on their travels this season.
"We look forward to getting Letchworth at our place and doing the business against them, we owe them one," added Brock.
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