Marin Cilic is not a new face in tennis.  He knocked Andy Murray off at the 2009 US Open when many felt Murray would breakthrough with a title.  Cilic reached his first Grand Slam semifinal at the 2010 Australian Open beating Juan Martin del Potro and Andy Roddick in succession prior to falling to Andy Murray in 4 sets.

Cilic is, however, younger than the Big 4/5.  Federer is 36, Wawrinka is 32, Nadal is 31 while both Djokovic and Murray are both 30.  Both Marin Cilic and Juan Martin del Potro are a youthful 29 years of age.  Unlike JMDP, Cilic has no major wrist issues impacting his two-handed backhand.  Cilic won the US Open in 2014, won Cincinnati in 2016, and reached the Wimbledon final in 2017.

It would be nice to see a player in his mid-20s or younger challenging the Big 4/5 with matches going back and forth until eventually, a few young lions take over the pride.  John McEnroe and Ivan Lendl were 7 and 8 years younger than Jimmy Connors as they tried to supplant him.  Stefan Edberg, Boris Becker, and Mats Wilander were all younger than McEnroe and Lendl.  Pete Sampras, Andre Agassi, Jim Courier, Michael Chang, and Goran Ivanisevic all challenged their elders.  There was a bit of a gap, but champions like Patrick Rafter emerged shortly before the New Balls generation crashed the scene.  Roger Federer is the last of the New Balls players, but he was challenged by Rafael Nadal’s rise to #2 in 2005.  By 2008, it looked like Djokovic and Murray were either winning or contending for majors.  Since 2008 Stan Wawrinka emerged as a late bloomer a la Patrick Rafter, but no one else has thrown down the gauntlet in a manner we might have expected.

Certainly, injuries prevented JMDP from making an all-out assault on the top ranking.  Then again, Pat Cash, Miloslav Mecir, Thomas Muster, Richard Krajicek, and Gustavo Kuerten could all have piled up many more big wins had injuries not interfered.  Injuries are not new and always claim a few potential greats along the way.

As it stands now, Grigor Dimitrov has shown signs of life but has not proven he can take the next step.  Dominic Thiem may win Roland Garros soon, but his game seems surprisingly limited on other surfaces.  Nick Kyrgios is too combustible right now (and maybe forever).  Sascha Zverev is seemingly still figuring out five-set matches.  The list could easily be expanded.  Tennis has no shortage of promising players under 29, but Cilic is a known and proven commodity.  Perhaps the oligopoly of the Big 5 ends through the continuing good results of a player like Cilic combined with the toll of injuries and age on the members of the oligopoly.

At this point, Cilic has had 11 quarterfinal or better finishes in majors and 17 career titles.  He has victories at majors over Murray (USO 2009), Federer (USO 2014), and Nadal (AUS 2018).  He may not be an all-time great or shoe-in for the Hall of Fame like the members of the Big 5 are, but he is good enough to make things interesting versus anyone.  That is what tennis needs.  If others follow his lead, we may get a less predictable tour.