Both these players can play on all surfaces to a very high level, including plenty of success on clay. Stosur has had far more of a career on the singles court than Vesnina who has had lots of doubles success recently. However the Russian is very capable of causing an upset and has a 2-2 H2H with Sam, including 1-0 on clay. Neither player have had consistency this year, but they are capable of beating the very best on their day. In the 1st round Stosur beat Lisicki and Vesnina over Svitolina, both very tricky opponents. This is a more even match than the bookmakers suggest and I think there is value for Vesnina, though only very low stakes. Both girls will need to serve well.