The former Formula 1 Canadian Grand Prix winner dominated his class in a Citroen DS3 RRC despite this being only his third gravel rally.
Despite his success he believes that lack of experience will ultimately count against him on future loose-surface rounds of the series.
Asked to rate the likelihood of a WRC 2 title push this year, Kubica said: "The chances are zero. I am not concentrating on it.
"I had no experience before Portugal, I had not driven on gravel and most rallies this year are on gravel.
"I am not thinking about the championship - I approach every rally like this. I like to go fast and bring the car to the limit, but rally is a lot of experience and I don't have any.
"I have good skills bring the car to the limit, but this is 10 or 30 per cent. The rest is experience of the roads and conditions and I am discovering these every time I come to the rally."
Kubica's next outing will be Rally d'Italia later this month.
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