A rare headed goal from Rivaldo earned Olympiakos Piraeus a 1-0 win over Akratitos which restored their six-point lead at the top of the Greek first division on Monday.
After 19 rounds, Olympiakos have 51 points with second-placed AEK Athens on 45. Panathinaikos are third with 39 points.
The top two meet next Sunday at the Karaiskakis Stadium in a match that may effectively decide the championship.
Olympiakos, who have now won 12 games in succession, had to work hard against the bottom club and it was not until the 68th minute that Rivaldo settled the game with his fourth goal in the last four league games.
Rising unchallenged to meet a corner from the left, Rivaldo headed the ball down into the bottom corner.
Grigoris Georgatos almost added a second but his shot was palmed by the Akratitos goalkeeper Sotiris Lymberopoulos on to the crossbar.