It all started to go wrong for out-of-form Olympiakos in the 38th minute when a long-range shot struck dfender Avraam Papadopoulos and skewed past Antonis Nikopolidis in the Olympiakos goal.
The home side got things back on track when Costas Mitroglou and Matt Derbyshire combined well a minute later for the Englishman to produce a neat finish to make it 1-1.
It got even better for the Reds when Derbyshire helped set up Lomana Lua Lua on the stroke of half-time for the Congo international to flick the ball over a PAS Yiannina defender and then poke it into the net.
Olympiakos only held on to the lead for nine minutes of the second half when another deflected shot, this time off Olof Mellberg, looped over a helpless Nikopolidis.
Mellberg almost made amends in the closing stages but hit the post instead and Olympiakos had to settle for just a point.
Although it moves them within four points of Panathinaikos (58 to 54), if the Greens win at Asteras Tripolis on Sunday they will be seven points clear of their rivals in third place, behind PAOK, with just four games left.
The draw helps move PAS Yiannina out of the relegation zone, at least temporarily, on goal difference.
Also on Saturday, AEK put in an impressive home performance to beat Kavala 3-0.
Ismael Blanco opened the scoring in the 35th minute with a penalty. Bosnian Sanel Jahic added a second on 50 minutes and Gustavo Manduca rounded off a good night for Dusan Bajevic's men with an 82nd minute goal.
The win means AEK have 45 points after 36 points and look set to hold on to fourth place ahead of the Champions League play-offs.
A little earlier in Athens, Atromitos beat Iraklis to essentially ensure their survival and to leave the Thessaloniki side still looking over its shoulder at the relegation zone.
Thanassis Karagounis opened the scoring for the home side in the 25th minute and Marek Saganowski added a second 10 minutes later with a powerful volley.
Grigoris Papazacharias reduced the deficit just before half-time with a long-range looping header but Iraklis were not able to rescue a point and suffered their first defeat since Jozef Bubenko took over seven games ago.
Atromitos have 35 points and should be considered well and truly safe while Iraklis, still on 31 - six above the relegation zone, are likely to need one more win.
Olympiakos's hopes of retaining its Super League title suffered a major setback on Sunday as the Reds lost 1-0 at Iraklis just after Panathinaikos had dispatched Levadiakos 3-0.
Having seen title rivals Panathinaikos and PAOK win, all the pressure was on Olympiakos to produce a stirring performance at the Kaftantzogleio Stadium but they came up against a spirited Iraklis and a goalkeeper in an inspired mood in Daniel Fernandes.
The on-loan Portuguese keeper was equal to everything that Olympiakos could throw at him in the second-half, when the Reds had more than 70 percent of the possession and create several clear chances.
Iraklis had taken the lead in the eighth minute when Swedish defender Olof Mellberg tripped Daigo Kobayashi in the box. Romanian Bogdan Mara scored from the spot to give the home side something to hang onto for the rest of the game.
Iraklis had Victoras Iacob sent off for a second yellow card during stoppage time - his third red card of the season - but it was too late to have an impact on the final result.
The defeat means that Olympiakos remain on 53 points, five behind Panathinaikos and three behind PAOK in second place.
The Reds now need nothing but a win when they face Panathinaikos in two weeks' time if they are going to have a chance of retaining their title.
The win moves Iraklis to 31 points, seven clear of the relegation zone.
Panathinaikos scored all their goals in a blistering 10-minute spell in the second half against Levadiakos to maintain their two-point gap at the top of the Super League table.
Panathinaikos took their time to break down some strong resistance from relegation-threatened Levadiakos at the Olympic Stadium in Athens.
A mixture of sloppy finishing, bad luck and desperate defending meant that the first goal did not come until the 65th minute when Dimitris Salpigidis struck.
Sebastian Leto, who had been a threat throughout the game, added a second in the 72nd minute and Djibril Cisse got his customary goal on 75 minutes, after missing a penalty.
The win moved Panathinaikos onto 58 points from 25 games. Levadiakos remain third from bottom on 24 points.
Panionios took a major stride towards securing their safety with a resounding 3-0 home win over Xanthi, who remain in deep trouble.
Bennard Kumordzi opened the scoring on 21 minutes and Czech defender Martin Latka added a second five minutes before half-time to put the home side in the driving seat.
Former Aston Villa striker Bosko Balaban rounded off the win on 61 minutes.
Panionios are on 31 points, seven clear of the drop zone, and can now begin to plan for another season in the top tier.
Things are less clear cut for Xanthi, who remain on 25 points - just one place and one point above the bottom three.
Xanthi's day was made even worse by the news that fellow strugglers PAS Yiannina had beaten Asteras Tripolis with an injury time goal.
Ibrahima Bakayoko got the vital goal to give the home side a 1-0 win that lifted them to 24 points and gives the team from northeastern Greece renewed hope of Super League survival.
Asteras had played the last 20 minutes with 10 men after the sending off of Adrian Bastia. The Peloponneseans are in 10th place.
The mid-table clash between Ergotelis and Atromitos ended 1-1 on Crete.
An own goal by Polish striker Marek Saganowski had given Ergotelis the lead in the 83rd minute but Atromitos have proved all season that they are made of stern stuff and it was no surprise when Stelios Sfakianakis scored an equalizer in the first minute of injury time.
Irrepressible Cisse fires PAO to top spot
Frenchman adds two goal to impressive tally
PAOK beat PAO to join title race
Greens lose 2-1 in Thessaloniki
Aris and Kavala reach Cup semifinals
They will face each other
PAOK get revenge on PAS Yiannina
Santos's men win in one of three away victories
Rain halts Aris v Panthrakikos, as AEK win
AEK and Kavala win in other games
PAO struggle before beating Kallithea
Greens reach cup semifinals
PAS Yiannina demolish PAOK in Cup
Epirus side win 4-0 to reach the semis
Papazoglou sends PAOK second
Wins also for Iraklis and PAS Yiannina
PAOK derail hopes of Reds revival
Visitors win 1-0, as PAO draw at Aris
Cup draw perfect for Panathinaikos
PAOK will face PAS Yiannina test
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