The Hoyas shot only 38 percent on their home floor and fell behind by 17 points at halftime.
Georgetown went into the Big East Conference season with an 11-1 record but the Hoyas have lost four of their first five league games.
Gibbs made five 3-pointers and scored 22 points. Brad Wanamaker added 14 points for the Panthers (16-1, 4-0 Big East). Pittsburgh won its sixth in a row.
Chris Wright led Georgetown with 14 points. The Hoyas made only 5-of-22 from beyond the arc in their third straight loss.