The first part of this double will be the match between Joao Sousa and Damir Dzumhur. Sousa is the rightful favourite in this match-up but I don't think he should be a short as 8/15 to win. Dzumhur leads the head to head 2-0 - both of these matches were pre-2014 though and both players have improved a lot since then.
Sousa has struggled for form this year, with a 12/16 win/loss record and has not been at his best in recent weeks on the clay. He did get to the semis in Nice last week but beat Kevin Anderson who has not much played much this season and then lost a match he should have won against a fatigued Alexander Zverev.
Dzumhur, on the other hand, has been in pretty good form, winning 12 of his last 18 matches and took the scalp of Berdych in Monte Carlo. He has a winning record on clay this year of 9/5 and will see this as a great opportunity to advance to the second round.
Both of these players have a similar style and neither are going to blow the other off the court. For that reason I can see this being a epic match, maybe going the whole way to five sets.
The second part of this double will see Zverev face Herbert for the fourth time in their careers. Herbert leads the head to head 3-0, however these were all on hard courts and Zverev has improved immensely since these matches, as shown by his 3/10 odds to win this one.
2016 has been an excellent year on clay for Zverev so far, with a 11/5 win/loss record, reaching the semi finals in Munich and the final in Nice. I do think he is being favoured a bit too much by the bookmakers, though. Having played so much tennis recently he may be a little jaded and I certainly don't see this match as being straight forward for him.
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Herbert has also had a decent clay court season so far with a 5/2 win/loss record. In those matches he has beaten some decent clay court players in Guido Pella and Mikhail Youzhny, while his two losses came in tight affairs against Andy Murray and Sam Querrey. While you would say Herbert is more suited to quicker courts I do think he is capable of winning at least a set against Zverev here.