Panathinaikos fell behind after seven minutes to a goal by Daniel Cousin at the Olympic Stadium but Djibril Cisse equalised for the Greens in the 22nd with his eighth of the season.
Luis Garcia had a chance to win the game but hit the post in the fifth minute of added time.
The point moved the champions level on 21 points with Olympiacos, who are scheduled to play the second half of their match with Ergotelis on Sunday, but Panathinaikos are top because of a better head-to-head record.
PAOK Salonika snatched a last-gasp 2-1 victory over AEK Athens, who had Kostas Manolas sent off, to leapfrog the Yellows into third place.
Vierinha struck in the fourth minute of added time to secure a win for the hosts who have taken 17 points from their opening 10 matches, one more than AEK.
Giorgos Fotakis had put PAOK ahead just before halftime before Leonardo levelled with a penalty after 68 minutes.