Ammerlaan nudged out Italy's Camilla Alessio who sat in the hot seat for the best part of an hour, the Dutch youngster coming home seven seconds faster on the 19.8km course. GB's Elynor Backstedt - the daughter of former pro cyclist and Paris-Roubaix winner Magnus Bäckstedt - rounded out the podium.
“There are no words," Ammerlaan said immediately after the race, adding a bit more in the later press conference.
“Two weeks ago I raced against some of my adversaries, so I knew I was in good shape. It’s great to race as a Dutch rider because you can learn a lot from the Elite champions who are the best in the world.
"In the summer we came here together to ride the time trial and the road courses. We did some training camps as a team. We get a lot of support which paid off today and I hope to have a good future in the Elite ranks next year.”
Australia's Sarah Gigante and Anya Louw finished the day 15th and 16th respectively.
Chilean Carmen Soto who races for Aussie domestic team Holden Gusto finished 14th.
Men's under 23 ITT
Defending under 23 ITT world champion, Denmark's Mikkel Bjerg backed it up again for this year's title, dominating second placed Brent van Moer (Belgium) by 33 seconds. He also bested compatriot and bronze medallist Mathias Norgard on the 27.8km course by 38 seconds, his almost brother-in-law.
“The course suited me really well," Bjerg said. “It was similar to Bergen, shorter but more explosive. We worked with our coach to be able to go really hard on the climbs and recover for being fast on the flat at the end."
Bjerg said despite the result going his way, there will be no totes awks feelings at family gatherings.
"Mathias and I train a lot together. I’m engaged to his sister. A good training environment has paid off today. Normally at the end of the season, it’s hard mentally, but we were able to push each other to perform this late.”
Aussie Callum Scotson performed strongly, finishing 10th.