Novak Djokovic is laying siege to Roger Federer's two-year rule of Rod Laver Arena, as the two tennis titans chase a record seventh Australian Open men's singles crown.
Federer, who faces Denis Istomin on Monday night to launch his quest for an Open hat-trick, has owned the Open since his stunning return to grand slam glory with an epic victory two years ago over Rafael Nadal.
But his latest reign coincided with Djokovic's mystifying slump during which the Serb dropped to No.22 in the world and was barely a factor at the majors.
Djokovic is undoubtedly back, the 31-year-old rediscovering his mojo in winning Wimbledon and the US Open in 2018 to regain the No.1 ranking and top seeding status for the Open.
Even after another Federer undefeated Hopman Cup campaign and a crushing victory over world No.4 Alexander Zverev - the German leading the next-gen challenge of trying to end the big three's grand slam domination - the great Swiss insists Djokovic is again the man to beat in Melbourne.
"No doubt about it, Novak is the favourite," Federer said.
Stranded on 17 slams for almost five years before his extraordinary renaissance in 2017, Federer always believed Djokovic would cool after his white-hot run and give him another grand slam look-in.
"He challenged me time and time again and I think I played him in his absolute prime, when he was virtually unbeatable, when he was hitting sliding backhand passing shots on the line time and time again," the Swiss said.
"So, for me, it was important not to get frustrated by it (and hope) that maybe it was just a moment in time."
But it's now apparent Djokovic's untouchable touch was no such "moment in time", with Federer declaring the 2019 model Serb back to his best after adding majors number 13 and 14 last year to his collection.
Between them, Federer and Djokovic have won eight of the past nine Australian Open titles, and 12 of the past 15, with Marat Safin (2005), Nadal (2009) and Stan Wawrinka (2014) the only gatecrashers to their annual Melbourne Park party.
No player has suffered more despair in Melbourne at the hands of the dominant duo than Andy Murray, the Brit losing five finals to Djokovic and Federer.
With the former world No.1 conceding this will be his last Open before retiring this year with chronic hip pain, the odds are long that Murray will get a sixth chance this fortnight to claim the Norman Brookes Challenge Cup.
"I hope that he can play a good Australian Open and he can keep playing beyond that, really finish the way he wants to at Wimbledon," Federer said.
"That's what I hope for him."
Slated to square off with Federer in the semi-finals, second-seeded Nadal also opens his campaign on Monday, the Spanish superstar playing Australian wildcard James Duckworth.