PARIS, June 20 (Reuters) - The party of French far-right leader Marine Le Pen came top in the first round of regional elections in the Provence-Alpes-Cote d"Azur region around Marseille, beating the incumbent centre-right into second place, according to an exit poll. The Rassemblement National"s Thierry Mariani garnered 33% of the vote, the exit poll showed, just ahead of the 30% won by the centre-right"s Renaud Muselier, who had struck an alliance with President Emmanuel Macron"s party.