The two men had gone back out in the dinghy and saw what they initially thought looked like a pillow floating in the water.
As they drew nearer, they realised it was the swimmer they had been talking to earlier lying face down in the water, she said.
Together, the two men managed to bring the swimmer to shore pumping his chest to clear his lungs as they rowed.
On shore, Ms Thompson began CPR - using the beat of Stayin' Alive to remember what to do.
"I hadn't done a CPR course for two years but the instruction room for CPR is next door to my office," said Ms Thompson, who works at Rotorua Hospital as a professional development unit administrator.
"They teach people on the CPR course to apply pressure to the chest by remembering the rhythm of Stayin' Alive," she said.
"I just remembered the rhythm as I gave him CPR.
"He was in a terrible way, he was a bad colour, his eyes were black and he was coughing up a lot of foam and water out of his mouth."
With help from others on the beach, she helped clear the man's airways, pushing on his chest for 10 minutes until paramedics arrived.
The swimmer, who had had a heart attack, was admitted to Tauranga Hospital and later discharged.
"At the time, we didn't think much about it but later that night it sunk in what had occurred," Ms Thompson said.
"It's not something we would want to go through every day."
She said she had booked to go on a CPR refresher course.
"Cardiac arrests, like this man, don't normally make it through because a lot of people lack the training - so it was good we were able to help him until the paramedics arrived.
"Anyone can do CPR and everyone can be trained to learn how to do it - I thought afterwards that while I had not been on a course for two years it was better to do something at the time to help him than nothing at all.
"We are just glad there were some really amazing people on the beach who all helped."