Nash (18,451) ended the night 4525 votes ahead of Nimon's 13,926.
It was a 695 reduction on his 5220 majority in 2017 over National candidate David Elliott.
The Labour Party also claimed the electorate's party, with 50.1 per cent compared to National's 28.8 per cent - a switch of the 2017 result which saw voters choose a Labour candidate but give National the party vote in the electorate.
Nash was based at the Gatsby Room at Napier's Masonic Hotel on the night, with Labour supporters packing it out and cheering loudly each time the party vote statistics flashed up on the TV.
Nash said he thought the Government's leadership and handling of Covid 19 may have been reflected in the party vote, and that people saw Jacinda Ardern to be genuine and compassionate.
"I think at this point in time New Zealand was looking for an inclusive Prime Minister that had a plan, as opposed to someone who was seen to be more divisive."
He said he was thrilled with Labour's party vote results both in Napier and throughout the country.
"A lot of these seats that we haven't held since 2008 look like they might be coming back to Labour."
First time candidate Nimon was overwhelmed by the support she received.
She watched the results come in from the Napier War Memorial and Conference Centre, where National hosted a low-key event with a few dozen supporters coming in over the night.
Early on in the evening, Nimon was hopeful that the traditional late surge of National election votes would close the gap on Nash, but it wasn't to be.
"People need to be confident that no matter what way it goes, I'll still be here for the next election," Nimon had said.
"You're not getting rid of me."
The statement confirmed Nimon's pledge a few days out from the election, that she was committed to representing Napier in the long-term.