The win lifted Beşiktaş to 84 points, level with Galatasaray who beat Yeni Malatyaspor 3-1. Besiktaş's goal difference of 45 was one better than their rivals. Third-placed Fenerbahçe ended on 82 points.
Croatian defender Domagoj Vida put Beşiktaş ahead in the 10th minute in İzmir, only for Alpaslan Öztürk to equalize for hosts Göztepe 14 minutes later. With the pressure rising as Galatasaray went ahead in their match, Beskitaş's Algerian winger Rachid Ghezzal, on loan from Leicester City, scored the winner from a penalty in the 69th minute.
The usual wild celebrations of champions in Turkey's largest city were muted, with the country under lockdown due to a recent surge in coronavirus cases.
The victory brought relief to Beşiktaş after a nervous end to the season, with defeats in their previous two matches. Last weekend they lost 3-1 away to Galatasaray, who won their final six games.