In what was described as the smartest display of riding on the international stage, Duncan showed some real skill and is just in front in the championships after the latest round in the Czech Republic.
She was third before the latest round but now leads Italian Kiara Fontanesi by three points and defending champion Livia Lancelot, of France, by seven points.
Coach Josh Coppins was extremely happy with Duncan's ride.
``She's improved hugely not necessarily as a faster rider but as a smarter rider, so that's what we have been working hard on,'' Coppins said.
``It's probably the best she has ridden for me at a grand prix since she started doing them. Finally, she took her time and was very calculated and patient. She understands she doesn't need to win every lap and every corner.
``She took her time to pick and choose the right moments to make passes and took her time to get the job done.''
The first race started out with Dutchwoman Shana Van der Vlist leading the way but she quickly dropped positions to the heavy hitters and title contenders. In the end, Duncan, came back from eighth place on the first lap to make a pass on Fontanesi only two corners before the finish, to take a superbly well-executed win.
``I got a terrible start, actually, and got pushed wide on the first corner and had to come from really far back,'' Duncan said.
``In my sighting lap I knew that it was really slippery, so I knew I just had to be patient on the first opening laps so I didn't risk any passes on the other riders. I found my way to fourth and then just took it from there.''
The second race started with a break from Belgian Armandine Verstappen who was chased hard by Duncan. She stayed on the back of Verstappen for the first half of the race before losing traction in a corner and going down and, while Duncan did not lose her position, she did drop 16sec off the lead.
However, she stayed second to the finish line to secure the championship lead.
Duncan will now look forward to her favoured hard sand conditions in the Dutch GP at Assen on September 9-10, the penultimate event in the women's world championship. The final round will be in France the following week.
