BRASILIA, Oct 1 (Reuters) - Former Brazilian President Luiz Inacio Lula da Silva holds a solid polling lead going into Sunday's election against incumbent Jair Bolsonaro, with a chance of clinching the race in the first round, fresh surveys showed on Saturday.Brazil's most polarized election in decades will decide whether to return to power the leftist leader who spent time in jail on corruption convictions or the right-wing populist who has attacked the voting system and threatened to contest defeat.Register now for FREE unlimited access to Reuters.comPollster IPEC showed Lula winning 51% of valid votes, excluding blank and spoiled ballots, and a Datafolha poll showed the popular two-term president with 50% of valid votes.Brazil's electronic voting system, which Bolsonaro has called vulnerable to fraud without providing evidence, allows the national electoral authority (TSE), to quickly tally results within hours after polls close at 5 p.m. (2000 GMT).The head of the TSE, Supreme Court Justice Alexandre de Moraes, called on Brazilians by Twitter to celebrate the country's democracy by turning out to vote with "peace, security and harmony, respect and freedom.""