The win over the Hawkeyes extended the Nittany Lions' nine-game winning streak and a perfect Big Ten record.
The Nittany Lions outshot Clarkson 81-48.
A 73rd minute go-ahead goal from captain Peter Mangione was the difference as the Nittany Lions gave Northwestern its first loss.
Sophia Gladieux scored two goals for her fourth multi-goal game of the season.
UMass is 1-6 this season, with its lone win being a 41-30 victory over New Mexico State.
