Mr Thomsen was watching and realised something had gone wrong.
"He didn't come back up and then people started to yell out that he's hurt. There was no one really near so him so I just jumped in the water and swam out. I just thought I had to get his head out of the water so he could breath.
"My first instinct was to jump in and swim out there and hold him out of the water. If someone needs help like that it's really a no-brainer."
Mr Thomsen jumped in to the water fully clothed and swam about 40 metres to reach Mr De Villiers, who was face-down and limp in the water.
"I got there and grabbed on to him and pulled his head up. Seeing his face, it was pretty scary."
Mr Thomsen and Scott Parry from the Fishing and Adventure TV Show held Mr De Villiers above the water until he could be loaded in to an inflatable rescue boat.
He was taken to Tauranga Hospital and then flown with an intensive care unit transport team to Waikato Hospital.
Adrian's wife Debbie De Villiers visited Mr Thomsen on Saturday to thank him for his actions.
"She said we literally saved his life," Mr Thomsen said.
"I'm just grateful he didn't die because otherwise I would have been thinking I didn't get out there quick enough."
Mrs De Villiers told the Bay of Plenty Times she saw the crash.
"If he had been under water any longer, it may have been a different result," she said.
Mr De Villiers suffered a blood clot on his brain in the crash.
Surgeons did not need to operate to relieve the pressure on his head and it was now a case of waiting to see if the clot liquefies and disperses itself naturally.
"Considering the crack on the head, he is doing really well. He is even talking about getting back to work," Mrs De Villiers said.
The only outward sign of injury was a black eye.
Mrs De Villiers said Adrian was feeling so well that he sent her out to buy chocolate and biscuits. He was expected to transfer back to Tauranga Hospital tomorrow or Wednesday.
The accident has persuaded her husband to wear a helmet in the future even although helmets were not normal for jetski stunt riders in New Zealand
"I will duct tape the helmet around his head if I have to," she said.
Mr De Villiers is considered the only jetski rider in New Zealand able to do back flips on flat water. The trick is the signature move of his performances.
- Additional reporting Bay of Plenty Times
