Tim Brent scored with 30 seconds left in the third period on Saturday night to give Wilkes-Barre/Scranton a 3-2 win over the Portland Pirates and a spot in the American Hockey League final.
The Penguins will battle the Chicago Wolves for the AHL's Calder Cup, with the series beginning in Chicago on Thursday. The Wolves defeated the Toronto Marlies in five games to advance from the Western Conference.
David Gove and Ryan Stone had given the Penguins a 2-0 lead in Game 7 of the Eastern Conference final after the first period but Portland stormed back with goals in the second from Stephen Dixon and Geoff Platt.
John Curry made 30 saves for the winners, with Jean-Sebastien Aubin stopping 37 shots for the Pirates.
Portland led 3-1 in Game 6 on Friday but allowed Wilkes-Barre/Scranton to storm back for a 4-3 overtime win.
The Penguins and their parent team in Pittsburgh have a chance to become just the fourth organization to win the Stanley Cup and Calder Cup in the same season. The last time the feat was accomplished was in 1995 with the New Jersey Devils and Albany River Rats.
The Montreal Canadiens and Nova Scotia Voyageurs both won championships in 1976 and 1977.