Bulgaria's centre-right GERB emerged as the winner of national elections on Monday but faced a struggle to form a government, suggesting no early end to the political stalemate that has gripped the European Union's poorest country. The party led by Boiko Borisov, which according to preliminary results won 31.4 percent of Sunday's vote, will have first chance to form an administration. But other parties said they were reluctant to cooperate with GERB, which resigned from government in February mired in allegations of corruption, and the second-place Socialists said they would look to ensure Borisov did not return to power. The often outspoken Borisov kept an unusually low profile following the vote and GERB - which held debt and spending low before quitting during nationwide protests - did not hold a post-election rally or make grandiose victory claims.