Institute of Public Affairs senior fellow John Roskam and KPMG director Sarah Overton will duke it out among a Melbourne Cup field of nine nominees to win Liberal pre-selection for the Warrandyte byelection.

The Liberals have held the seat, in Melbourne’s north-east, since 1988, but a loss at the byelection, brought on by the resignation of veteran MP Ryan Smith, would spell disaster for Opposition Leader John Pesutto and the party, which Daniel Andrews this week derided as “completely irrelevant”.