The Reds' advantage over second-placed PAOK Salonika was cut to eight points after an absorbing encounter in which both teams missed chances.
Atromitos, third in the standings and 17 points behind Olympiakos, were the last team to beat the runaway leaders in the league and Michel's team have won 17 of their 19 matches this season.
"The important thing is that we remain unbeaten and that's how we want things to stay until the end of the season," Olympiakos goalkeeper Roberto told reporters.
"We want to win every game and when you manage to stay unbeaten then such records win titles, it's that simple."
The champions were boosted by the return to action of striker Kostas Mitroglou ahead of next month's Champions League last-16 tie with Manchester United.
PAOK beat Panetolikos 1-0 at home through a solitary strike from Lucas and Panathinaikos stayed fourth by beating Panionios 1-0 at home thanks to a goal by Danijel Pranjic.