The leader on the Dutch centre-left D66 party, Rob Jetten, claimed a "historic" result after an exit poll put his party in a slight lead in the Netherlands' general election.
The poll showed D66 narrowly leading the far-right party of anti-Islam lawmaker Geert Wilders.
If confirmed, the result could lead to a shift in government back towards the centre for the western European country, after a far-right government led by Wilders' party won the last election.
Jetten said: "We have shown not only to the Netherlands but also to the world that it is possible to beat populist and extreme right movements."
However, cobbling together a coalition that can command a majority in the 150-seat House of Representatives will be difficult in a parliament divided between left and right.