SANTIAGO, Nov 6 (Reuters) - Chilean right-wing presidential front-runner, Jose Antonio Kast, has retained his grip on first place in pre-election opinion polls ahead of leftist Gabriel Boric, as pollsters go into a legal blackout period two weeks before the Nov. 21 election. The Pulso Ciudadano poll, released on Saturday by consultancy Activa Research, had lawyer Kast on 27.3% of the vote versus 23.7% for Boric. In third place was Christian Democratic senator Yasna Provoste with 13.5%. Last week the same study said Kast had taken the lead in its first round poll, but appeared to be behind in a likely second round. If no candidate gets an absolute majority, there would be a vote in December to choose between the top two. The Cadem opinion poll, which surveyed 1,010 people, gave 25% of the vote to Kast and 19% to Boric, a 35-year-old congressman and former student leader. Many of the top candidates are in isolation after Boric tested positive for the coronavirus. The Cadem poll showed Kast, whom his adversaries compare with Brazilian President Jair Bolsonaro, gaining 44% of the vote in a hypothetical head-to-head against Boric, who it had on 40% in a second round vote.