Olympiakos beat Aris at home and extended its lead at the top of the Super League table to eight points, as AEK stumbled at Tripoli against Asteras.
A second-half header by Pape Cisse sufficed for Olympiakos to beat Aris 1-0 on Sunday at the Georgios Karaiskakis Stadium and claim the unofficial title of the winter champion at the halfway point of the regular season.
The Reds are now on an impressive 35 points from 13 games, still unbeaten, and eight points ahead of their main challenger, AEK, that shared a goalless draw with host Asteras Tripolis on Saturday.
PAOK is a further five points behind, having come from 1-0 down to beat visiting Lamia 2-1 a Toumba. Bachana Arabuli gave Lamia an early lead before Lefteris Lyratzis and Jasmin Kurtic gave PAOK all three points.
Also on 22 points is surprise package PAS Giannina, that fought back twice from a goal down to beat Volos 3-2. However the second Volos goal by Sotiris Ninis, a sideways bicycle kick from 15 yards out, is a strong candidate for goal of the season.