Since 2008, the ATP Tour has been dominated by the Big Four: Roger Federer, Rafael Nadal, Novak Djokovic, and Andy Murray. They've controlled the rankings, majors, and ATP 1000 Masters Tournaments with little opposition from the rest of the tour. 2016 however, has shown their reign to be in decline and it is especially obvious in this year's US Open. Federer pulled out of the tournament due to injury, Nadal was upset by world-number 25 Lucas Pouille in the fourth round, Murray (the reigning Olympic champion) was edged by world-number 7 Kei Nishikori in the quarter-finals, and Djokovic cruised his way into the finals with two retirements and one walkover. Although it is unsure whether the Big Four will ever once again dominate the tour, it does make tennis fans wonder: who's going to take their place? As the final slam of the year comes to a close, here are three players who could possibly dethrone the Big Four and win their first major in the next few years.

1. Kei Nishikori

The top Japanese player in the world already has 11 titles and reached the US Open finals in 2014. Nishikori's quarter-final win over Murray showed that he has the firepower, mental fortitude, and exceptional shot-making ability with his ground-strokes to go toe-to-toe with the Big Four. With Nadal and Federer's careers reaching their final years, it would be no surprise to see Nishikori take their place.

2. Gael Monfils

Known for his theatrics and trick shots, Monfils showed the tennis world that he has the skill and experience to make deep runs into the second week of the majors. Although falling to Djokovic in the semis (in undoubtedly the strangest match of the Open this year), Monfils showed consistency and focus that hadn't been seen since his last semifinal appearance in the 2008 French Open. The Frenchman already has a blistering forehand and unrivaled athleticism, but a little push in mental consistency would reward Monfils with his first grand slam.

3. Grigor Dimitrov

Nicknamed "Baby Fed" for his similar groundstrokes and service motion to Roger Federer, the Bulgarian has had bit of a rough 2016. With several first- and second-round losses earlier this year, the world-number 24 has made significant strides in the latter half of the season with a semi-final run in Cincinnati and a run to the round-of-16 in Flushing Meadows. Dimitrov has a strong serve, a powerful backhand, and great touch at the net. With good coaching, a healthy mindset, and a favorable draw, the world could see Dimitrov winning his first slam in the next few years.