After the final whistle, hundreds of Fenerbahçe fans occupied the pitch at their Şükrü Saracoğlu Stadium in İstanbul. Others broke off plastic chairs and threw them at police, who tried to use their shields to protect the players. Flares were also tossed at the police.
In response, police used pepper spray to disperse angry Fenerbahçe fans and evacuated the stadium as the players escaped to changing rooms along with police.
The fans also threw chairs and other objects at a corridor leading to the changing rooms. The clash followed a tense game during which referee Cüneyt Çakır booked several players and issued red cards to one player from each team.
Sports channel Lig TV said journalists, players and even policemen were also affected by the pepper spray. Some parents angrily reacted to the police after their children were affected, the Anadolu news agency said.
Lig TV said some Fenerbahçe fans also clashed with police outside the stadium, throwing stones at a police vehicle that had a water cannon.
The fans also turned over two police vehicles and set them on fire in İstanbul's Kadıkoy district. Police and citizens nearby quickly put out the fire. The fans also turned over garbage cans and shattered shop windows, also leaving behind streets littered with fist-sized stones.
In related violence elsewhere in the country, a 40-year-old man was killed by celebratory gunfire in the northern Turkish province of Giresun in the first reported death directly linked to Saturday's derby match. In İstanbul, a 29-year-old man wearing a Galatasaray jersey was stabbed in the abdomen in an attack by Fenerbahçe fans on Saturday, but he was reported to be in stable condition.
Kemal Aycı was shot in the head when an unidentified man shot into the air to celebrate Galatasaray's win in Giresun's Görele district. Aycı's body was taken to Görele State Hospital morgue.
More clashes erupted between Fenerbahçe and Galatasaray fans in İstanbul and other cities.
The pitch invasion and violence at Şükrü Saracoğlu Stadium blocked Galatasaray from immediately celebrating its 18th league title and lifting the Turkish Super League Cup. Authorities finally turned off the floodlights.
Galatasaray eventually returned to the field and received the trophy under the lights of television cameras -- soon after Prime Minister Recep Tayyip Erdoğan, who is a member of Fenerbahçe's general assembly and a former football player, said the ceremony should be held on the pitch, state television said.
Coach Fatih Terim earlier said his team "would not leave without taking the cup." Terim was reportedly opposed to receiving the cup in the changing room.
Tens of thousands of Galatasaray fans took to the streets, honking car horns across the country, dancing in the streets and chanting slogans, just days after the Turkish Football Federation cleared all teams implicated in an alleged match-fixing scheme, drawing criticism even from some federation officials.
Many other Galatasaray fans celebrated the Lions' victory as champions of the 2011-2012 season early on Sunday at the Florya Metin Oktay facilities.
After winning the title, Galatasaray coaches, staff and footballers left Fenerbahçe Şükrü Saracoğlu Stadium singing and chanting in celebration. Later, they arrived at the Florya facilities, where thousands of their fans enthusiastically greeted them.
“Here are the fans, here are the champions. Why not fix matches, why not fix matches, why not fix matches, [Fenerbahçe Chairman] Aziz Yıldırım,” shouted the fans in reference to an extensive match-fixing probe into Turkey's football clubs.
The Galatasaray coach, whom Lions fans called “Emperor Fatih Terim,” cheered and waved the newly won trophy from the balcony.
It was not clear if UEFA would be satisfied with the decision of the federation, which only sanctioned some players and club officials but spared the clubs, including Fenerbahçe, which was allegedly at the center of the match-fixing scandal.
The match-fixing controversy also comes amid Turkey's bid to host the 2020 European Championship, which puts Istanbul's bid for the 2020 Olympics under more scrutiny.
It's unlikely Turkey would be granted both events. The International Olympic Committee (IOC) would award the Olympics to İstanbul only on condition Turkey would not also stage the football championship in the same year.
The government has so far fully supported both bids.
Also bidding for the 2020 Olympics are Madrid, Tokyo, Doha and Baku, Azerbaijan. The IOC executive board will announce on May 23 the list of finalists. The full committee will select the host city in September 2013.