Del Potro's been playing very well on clay but so has Berdych. Berdych's only loss on clay this year was to Djokovic at Monte Carlo. DP hasnt lost on clay this year but none of those wins have come against top tens.
I cant see DP straight setting Berdy on this one. Berdy moves unbelievably well for a big man on clay. I think Berdy at +145 is good value. I'll back it up with an over 22.5 play.