It was 8-4 to the Swede, who took Olympic bronze in Rio de Janeiro in 2016, who wrestled for the first time in almost a year.
Mattsson controlled basically the entire match and had a 5-0 lead with one minute left.
On the way to the final, the European Championship runner-up from last year, Nina Hemmer, Germany, was defeated.
Johanna Lindborg was third in 57 kg.
Jonna Malmgren in 50 kg was also third.