“It's definitely a defeat for us. Losing Rome and Turin is a blow, it's painful,” Matteo Orfini, president of the Democratic Party (PD), said in an interview with La Stampa daily.
   
The city elections have been a closely-watched barometer of Italian politics.
   
Renzi's political strength has weakened in recent months. Rome in particular is seen by some analysts as a springboard for general elections due in 2018.
   
Sunday's polls saw the populist Five Star Movement (M5S) sweep to power in the capital and in the northern industrial city of Turin.
   
Virginia Raggi, 37, was elected as Rome's first female mayor, trouncing the PD candidate, Roberto Giachetti, in a 67-to-33 percent share of the vote.
   
The anti-establishment M5S also claimed control of Turin, where another woman, Chiara Appendino, 31, took 54.56 percent, ousting the long-serving mayor, Piero Fassino, a PD heavyweight.
   
The PD had some satisfaction by winning in Milan, Italy's principal economic hub, against a centre-right opponent.
   
Orfini said the results from the various cities bore out M5S's tactics, of forging local alliances with rightwing or far-right candidates to gain the votes of their supporters for the second round of voting.
   
The PD's leadership is to meet on Friday to analyse the outcome of the elections, Orfini said.