Fenerbahce suffered just their second Turkish Super Lig defeat of the season as they lost 2-1 to Karabukspor on Sunday.
Ilhan Parlak's penalty stunned the league leaders after Emmanuel Emenike's seventh league goal of the season had cancelled out Joseph Akpala's opener.
Karabukspor climbed to seventh with the victory, their third in a row in the Turkish top flight.
Second-placed Kasimpasa had already been held to a 0-0 draw at Rizespor on Friday.
Besiktas, Galatasaray and Eskisehirspor were the beneficiaries of the top two's failure to win over the weekend.
All three took maximum points to close the gap at the summit, with Besiktas 4-1 winners against Elazigspor.
Burak Yilmaz scored both of Gala's goals in a 2-1 triumph over 10-man Trabzonspor.
And Eskisehirspor also took advantage of having an extra man in their 2-0 victory versus Gaziantepspor.
Elsewhere, Kayserispor and Konyaspor drew 0-0, and Genclerbirligi beat Antalyaspor 3-2 away from home.
Bursaspor continued their revival with a 3-1 win over Kayseri Erciyesspor on Monday.
Ferhat Kiraz set the tone with the opener after just three minutes to put the hosts on course for a fifth game unbeaten in the league.
A rare Serdar Aziz strike doubled Bursaspor's advantage, but Senijad Ibricic's penalty before the break brought the visitors back into the game.
However, Slovakian Stanislav Sestak wrapped up the result eight minutes after the interval to move resurgent Bursaspor into the top half.
Sivasspor, meanwhile, are suffering a loss of form after they slumped to a late 2-1 defeat at Akhisar Belediyespor.
Kerim Zengin's stoppage-time strike inflicted the visitors' third defeat in five league matches after Umit Kurt had been given his marching orders.
It had started so well for Sivasspor, with Burhan Eser handing them the lead after 30 minutes.
But Mehmet Akyuz levelled before the break and Kurt's moment of madness was followed by Zengin's late and decisive effort.