The Big Four is Back: Andy Murray returns to the ATP's quartet

A year after falling out of the ATP's top four rankings last year, Andy Murray is back at No. 4 after his run to the Australian Open final last week. The surge reunites the ATP's Big Four at the top of the rankings, with Australian Open champion Novak Djokovic at No. 1, Roger Federer at No. 2 and Rafael Nadal at No. 3. Kei Nishikori rounds out the top five. Last year's Australian Open finalist Stan Wawrinka, who lost to Djokovic in the Australian Open semifinals, falls to No. 9. 

Fifty parting thoughts from the Australian Open

After his run in Melbourne, 19-year-old Nick Kyrgios surges up 18 spots to No. 35, almost assuring a Top 32 seeding at the French Open and Wimbledon. Kyrgios, who is taking two weeks off to rest his back, has just 175 points to defend from now until Wimbledon. Fellow Aussie Bernard Tomic also took an 18-spot jump after making the fourth round, up to No. 48. Another Aussie, Sam Groth, is up to No. 70 after his run to the third round. 

On the American front, John Isner is back in the top 20 at No. 18 after a third round run in Melbourne. Steve Johnson is in the No. 2 American slot at No. 37, while Sam Querrey fell seven spots to No. 42. 

More notable moves:

• Milos Raonic matches his career-high ranking, moving up two spots to No. 6. Tomas Berdych (7), Marin Cilic (8), Wawrinka (9), and David Ferrer (10), complete the Top 10. 
• Viktor Troicki continues his comeback. He's back in the Top 50 at No. 46 with nothing to defend until July. 
• Biggest riser in the top 100: Daniel Gimeno Traver. He jumped 21 spots to No. 89 by winning the Bacaramunga Challenger in Colombia. Sometimes it pays to skip the Australian Open.
• Biggest riser in the top 200: Jared Donaldson. The 18-year-old American is making his Top 200 debut after winning the Maui Challenger last weekend and rising 78 spots in the rankings. 
• Eight teenagers entered the top 200 for the first time since October 22, 2007, with Kyrgios, Borna Coric, Alexander Zverev, Thanasi Kokkinakis, Donaldson, Hyeon Chung, Yoshihito Nishioka and Elias Ymer making history in the rankings.