Ferreira, 65, was taken into an Athens hospital on Saturday due to a chest infection and was and kept in overnight as a precaution after developing pneumonia.
The Portuguese's team fell behind after just nine minutes at Panionios through Malta striker Andre Schembri.
A Sebastian Leto penalty and a Kostas Katsouranis goal from a tight angle in the second half allowed Panathinaikos to clinch victory and maintain third spot in the standings with 26 points from 11 games.
"The whole technical leadership, management and players would like to dedicate our victory to Jesualdo Ferreira and he is happy that everything is running smoothly," said assistant coach Jose Gomez.
"We showed solidarity and unity and kept our faith in being able to get the victory and we keep our faith that we can also win the championship."
Despite Panathinaikos' win, AEK Athens stayed on top of the league following a 2-1 home success against PAS Giannena on Saturday.
AEK have 28 points from 13 games, while Olympiakos are second with 27 points from 12 games after Marco Pantelic scored all four goals in a 4-0 thrashing of Kerkyra.
