Brendan Bean surrendered a walk-off two-run homer on Friday, allowing Winthrop to beat Penn, 11-10.
The Quakers had a six-run advantage heading into the bottom of the eighth, but the Eagles threw up a five-spot as Penn reliever Edward Sarti surrendered five hits and recorded just one out.
Things unraveled further for Penn in the ninth when Wyatt Henseler committed an error, allowing the tying run to reach base to open the frame. Bean then surrendered a two-run shot that doomed the Quakers.
Henseler finished 2-for-4 at the plate with four RBI for the Quakers. Andrew Hernandez hit a grand slam while Ben Miller also homered and drove in two runs.
The two clubs will resume their weekend set on Saturday.