H2H is 4-4 on clay but we have to look at the context.
Monaco 2006 was one of Djokovic's first M1000. He was a rookie, ranked #67.
Monaco 2008 was a walkover.
Monaco 2014 Djokovic had a wrist injury and tanked the match.
Djokovic won FO 2012, Rome 2012, Rome 2015 and Rome 2009 fair and square.
He straight-setted Nadal in every single clay events, Monaco Madrid Rome and RG.
The only time Federer straight-setted Nadal on clay was after the 4h10 match in the Semifinal of Madrid in 2009. He could thank Djokovic for that.
FO 2011 was a great match but that's all it was... One match. Overall, Djokovic is just a better clay player. Federer never winning Monaco or Rome is a glaring hole.