Medipol Başakşehir beat Beşiktaş 1-0 to move to the top spot in the opening game of the week 22 of Turkish football league Friday.
Former Beşiktaş striker Demba Ba scored for Başakşehir in minute 50.
After two consecutive wins under new manager Sergen Yalçın, Beşiktaş suffered its first loss.
Turkey's premier football league is set for riveting action as seven title contenders face at least one other challenger within a week.
The top seven are separated by just six points and fixtures this weekend and next could prove decisive in the title race.
Sunday will witness a top-of-the-table clash between Sivasspor and Trabzonspor.
The two sides have a one-point difference as Sivasspor have 42 points, however, Trabzonspor have a game at hand.
Sivasspor will also kick off next week's against fourth-placed Aytemiz Alanyaspor on Friday, followed by Beşiktaş and Trabzonspor's on Saturday.
Reigning champions Galatasaray, currently in the fifth spot, will take on sixth-placed rivals Fenerbahçe on Sunday.
There will be more than bragging rights up for grabs in the derby as the bitter foes are just a point apart in the table.
