Shields, who has yet to let a goal in at home, recorded seven saves against Penn.
Her most impressive save was in the first half when Ellen Gregory blasted a shot from well outside the 18 toward the top of the goal. Shields got a hand on the ball and tipped it off the crossbar.
The Harvard defense suffered one casualty in the 16th minute when freshman midfielder Rachael Lau went down with a sprained ankle. Sophomore back Daniel Mirabel stepped in for Lau and later subbed out for freshman back Tyler Press.
Later, senior midfielder Allison Kaveney took over at the position, starting both the second half and both overtimes.
Around the rest of the Ivy League on the opening weekend, Cornell defeated Columbia 1-0, Dartmouth handed Brown a 1-0 defeat, and defending Ivy champion Princeton fell to No. 24 Yale 2-1.
The Crimson has a full week to prepare for its matchup against the Bulldogs in New Haven on Saturday.
—Staff writer Carrie H. Petri can be reached at cpetri@fas.harvard.edu.