McEnroeisanartist
Hall of Fame
Looking at all the occasions in Grand Slams that the Big 3 could have played a match if the other player had won their match:
Federer-Djokovic
2006 Wimbledon - Ancic def. Djokovic, if Djokovic had won he would have played Federer in Quarters
2009 Australian - Roddick def. Djokovic, if Djokovic had won he would have played Federer in semifinals
2009 Wimbledon - Haas def. Djokovic, if Djokovic had won he would have played Federer in semifinals
2010 Australian - Tsonga def. Djokovic, if Djokovic had won he would have played Federer in semifinals
2011 Wimbledon - Tsonga def. Federer, if Federer had won he would have played Djokovic in semifinals
2013 Australian - Murray def. Federer, if Federer had won he would have played Djokovic in finals
Nadal-Federer
2004 Australian Open - Hewitt def. Nadal, if Nadal had won he would have played Federer in 4th Round
2008 US Open - Murray def. Nadal, if Nadal had won he would have played Federer in finals
2009 US Open - Del Potro def. Nadal, if Nadal had won he would have played Federer in finals
2013 US Open - Robredo def. Federer, if Federer had won he would have played Nadal in quarterfinals
Nadal-Djokovic
2008 Australian - Tsonga def. Nadal, if Nadal had won he would have played Djokovic in the finals
2010 French Open - Melzer def. Djokovic, if Djokovic had won he would have played Nadal in semifinals
2010 Wimbledon - Berdych def Djokovic, if Djokovic had won he would have played Nadal in finals
2011 Australian Open - Ferrer def Nadal, if Nadal had won he would have played Djokovic in the semifinals
Obviously, I did not count occasions where a Big 3 player defeated another Big 3 Player preventing the loser from playing the other Big 3 Player.
Federer-Djokovic
2006 Wimbledon - Ancic def. Djokovic, if Djokovic had won he would have played Federer in Quarters
2009 Australian - Roddick def. Djokovic, if Djokovic had won he would have played Federer in semifinals
2009 Wimbledon - Haas def. Djokovic, if Djokovic had won he would have played Federer in semifinals
2010 Australian - Tsonga def. Djokovic, if Djokovic had won he would have played Federer in semifinals
2011 Wimbledon - Tsonga def. Federer, if Federer had won he would have played Djokovic in semifinals
2013 Australian - Murray def. Federer, if Federer had won he would have played Djokovic in finals
Nadal-Federer
2004 Australian Open - Hewitt def. Nadal, if Nadal had won he would have played Federer in 4th Round
2008 US Open - Murray def. Nadal, if Nadal had won he would have played Federer in finals
2009 US Open - Del Potro def. Nadal, if Nadal had won he would have played Federer in finals
2013 US Open - Robredo def. Federer, if Federer had won he would have played Nadal in quarterfinals
Nadal-Djokovic
2008 Australian - Tsonga def. Nadal, if Nadal had won he would have played Djokovic in the finals
2010 French Open - Melzer def. Djokovic, if Djokovic had won he would have played Nadal in semifinals
2010 Wimbledon - Berdych def Djokovic, if Djokovic had won he would have played Nadal in finals
2011 Australian Open - Ferrer def Nadal, if Nadal had won he would have played Djokovic in the semifinals
Obviously, I did not count occasions where a Big 3 player defeated another Big 3 Player preventing the loser from playing the other Big 3 Player.