By Michele Kambas and John Stonestreet ATHENS (Reuters) - Greek leftist Alexis Tsipras made a last call on Sunday for weary voters to return him to power in a close-fought election, after a tumultuous year that saw him cave in to European demands for austerity to keep the country afloat. Both Tsipras and his conservative rival Vangelis Meimarakis, vying to take on the daunting task of steering the country through a refugee crisis as well as painful economic reforms, called for a high turnout as they cast their ballots in an election polls suggest is too close to call. It is the third time Greeks are voting this year, after an election that catapulted Tsipras to power and a referendum in which voters backed him to spurn the terms of a European bailout - only for him to agree to it anyway.