Lifeguard Fraser Harvey said they fished the man out and took him back to their base for "a stern telling off".
Mr Harvey said the man had been drinking but was not overly inebriated.
"It was really dangerous of him because he very nearly clipped his head on one of the arms," he said.
The acting general manager of St John's northern region, Gary Salmon, said it was a very big night for staff, one of whom was assaulted.
"There was the normal frontline activity - including the pedestrian who was hit in Pt Chevalier - but most of the surge activity was in central Auckland, where there was a number of assaults and people suffering alcohol impairment."
He said the patients' complaints were generally minor.
In the fan zones 93 people were attended and five were taken to hospital.
At Eden Park, 40 people were treated, including three who were taken to hospital.
Mr Salmon said there had not been time to analyse the figures in detail but they appeared to be minor issues.
People experienced chest pain but there were no heart attacks he knew of during the last minutes of the final.
During the World Cup tournament, St John staff had seen 1700 patients in fan zones and stadiums around the country.
"In general the crowds were relatively well behaved but unfortunately we did have an ambulance officer assaulted. Not seriously, but we were disappointed in that."
The assault happened in central Auckland but he did not have details.
"It was all wrapped up pretty quickly, but in general they were well behaved and in a happy and cheerful mood.
"It was just we were very, very busy."
Police said 46 people were arrested mainly for disorder and breaching the liquor ban throughout the central city.
However a spokesman for police northern communications said that was not a particularly heavy night, especially given the large numbers of people.
"It sounds like a well-behaved crowd."
- additional reporting APNZ
