But to view his victory only as a win for the opposition overlooks the countless mistakes Erdogan's ruling Justice and Development Party (AKP) has made in the run-up to the elections.

Coupled with a struggling economy, a political system that has in recent years skewed toward one-man rule and allegations of municipal corruption, voters sent a warning to the AKP that it is not invincible. The election showed that even Erdogan, whose personality is the driving force behind his party, can be defeated.

Erdogan has cast a long shadow over Turkish politics during his 16 years in power. He has consolidated power in his person to the detriment of Turkish democracy, but his legitimacy is based on his uncanny ability to win elections.

The President was not a candidate in this election, but the loss is still personal. Istanbul is his birthplace and the city where he launched his political career.

The opposition hopes that in Imamoglu they have found a political charisma to rival Erdogan's. Imamoglu's hopeful campaign messages and his calm and measured demeanor presented voters with an alternative they have not seen in a long time.

The opposition in Istanbul is celebrating, but the secondary governing body, the Istanbul city council, is still controlled by the AKP.

This may yet prove to be a challenge to both: Imamoglu may have to navigate a potentially obstinate council and the AKP will have to prove that they can be effective in the opposition.

In his victory speech Imamoglu told his supporters: "Of course you will be happy. But being happy does not mean breaking anybody's heart. This is not a victory, this is a new beginning."

His victory may very well signal a shift in the political dominance President Erdogan and his party have grown accustomed to.