Winner of Aus open has the following market :

Nadal : 2.66
Djokvic : 2.06
Murry - 7

You could bet Nadal and Murry with $86 to return $100. Roughly odds of $1.16

You could lay Murray at to return the same amount for a liability of $84. So roughly odds of $1.19

This can make the diff in a long term profit or loss. Same bet. Siilar liability, better odds.

These are before commission.