The anti-graft We Continue The Change party (PP), launched only two months ago by two Harvard-educated entrepreneurs who served as interim ministers, won 25.5% of the vote, based on 93% of ballots counted from Sunday's election, Bulgaria's third this year.
After two previous elections in April and July produced an inconclusive outcome, Bulgarian voters are keen to see a new government formed quickly to tackle a dire COVID-19 situation, surging energy prices and widespread graft.
"I voted for what we are fighting for and hoping to happen - a more serious change in everything, so that we can have a better life here, at least for our children," Kostadin Manov, a 39-year-old father of two, said after casting his vote in Sofia.
"This corruption and all this theft should stop."
But the partial results show the next parliament will be even more fragmented than in April and July, with seven parties represented.