LISBON (Reuters) -Portugal's far-right, anti-establishment party Chega overtook the centre-left Socialists to become the main opposition party for the first time on Wednesday after the final tally of ballots from abroad in a May 18 snap parliamentary election. The centre-right Democratic Alliance of Prime Minister Luis Montenegro won 91 seats in the 230-seat single-chamber parliament, including two from out-of-country voting. On the election night, the Socialist Party (PS) emerged slightly ahead of Chega in terms of the share of the vote but with the same 58 seats.