What is the point of a second ballot now?

Polls suggest Chirac will win with 78-80% of the total vote in the second ballot in a fortnight's time. And this is because he's up against Le Pen; if he'd been up against Jospin (who came within 1 to 1.5% of coming second), it would have been 50-50 or thereabouts. There's something seriously wrong about a system that lets this happen.