Elizabeth Pluimers has extended her lead in the Australian Ironwoman series.

The Northcliffe girl overtaking clubmate and close friend Kristyl Smith after a dominating performance during round four, in Perth on Sunday.

The narrow four-point lead means Pluimers and Smith are the only ones who can win the series from here.

Meantime, Caine Eckstein won the men's round, finishing almost three minutes ahead of fellow Queenslander Ali Day.

But Day holds onto the overall lead.