From 2007 until today Novak Djokovic managed to defeat his two rivals Roger Federer and Rafael Nadal in the same event in five tournaments. An incredible goal, also considering that there are rare cases in which the Big Three can compete with each other more than once in a single tournament.
The first double triumphed came at the 2007 Rogers Cup: in the semifinal Nole defeated Nadal, while in the final he won against Federer. The event took place again at Indian Wells 2011, four years later: in the semifinal he overcame Federer in the semifinal and in the final he beat Nadal.
Same year: at the 2011 US Open, Djokovic once again won in the semifinal against Federer and in the final against Nadal, winning his first US Open title. The last two times happened in London. At the 2013 ATP Finals, Nole first beat Federer in the round robin, then he defeated Nadal in the final.
Situation opposite at the 2015 ATP Finals: in the semifinal he defeated Rafael Nadal and in the final he beat Roger Federer. We can see how these tournaments are obviously either ATP Masters 1000, or Slams or ATP Finals. At the US Open 2011 came the only eventuality in a Major during which Djokovic managed to defeat both of his rivals.
This once again underlines how rare are these combinations. We have to also remember that Novak Djokovic leads in head-to-head against Roger Federer (27-23) and against Rafael Nadal (29-26): considering that he can reach and overcome both his rivals in the Slam Race, can he already be considered the GOAT?