Novak Djokovic -4.5 at odds 2.16
ATP - SemiFinal of World Tour Finals in London (England)
Novak Djokovic is actually in the 1st position in ATP ranking while Juan Martin Del Potro stands in the 7th position.
These two players have played eight times against each other and Novak Djokovic had done very well to beat Juan Martin Del Potro in six from those eight matches by proving that he does know very well the Argentinian.
The last time that these two players have played against each other was in US Open this year and Novak Djokovic did very well to beat Juan Martin Del Potro in three sets with the result 6-2 7-6 6-4.
I believe that Juan Martin Del Potro was able to beat Roger Federer in the third match of the group in this tournament because the Swiss was not so motivated but it would be completely different thing today.
In my opinion Novak Djokovic would be very motivated to end this season in the best way so i expect him to beat Juan Martin Del Potro quite easy and clear.