The Dunedin rider claimed victory in the Mantua leg of the FIM Women’s Motocross World Championship yesterday.
It leaves the overall series defending champion just four points off the top spot with one meeting left.
Duncan finished second, one second behind series leader Nancy van de Ven in the first race, before completing a dominant 19sec victory in the second race.
It was a strong comeback after a disappointing last race in which she suffered a "pretty nasty crash".
"I’m so stoked with today – the moto win and the overall," she said.
"Making up the points was great but to be honest with you, the thing I was most proud of was how I was able to forget about what happened on Sunday, regroup and to come out and put a performance like that in.
"It makes me really proud — for the team and for everyone that supports me. It’s great.
"Obviously I needed to as well.
"It was quite bad. I was 14 points down. It was important that I made it up."
The final round will be held on November 1 and Van De Ven leads Duncan by just four points.
The gap of five weeks until the final round suits Duncan well.
"That’s great for me because it gives me more time with the team, more time to test and more time to put some work in with the [Kawasaki KX250] 21.
"Having some extra weeks is going to be great.
"I think I can really put a good stint in there and make a lot of improvements."
