Now that he's back the Australian Open semi-finals, after a mystifying two-year funk, Novak Djokovic's rivals ought to be very concerned.
Djokovic already has six titles at Melbourne Park, equal to Roger Federer's haul and one short of Serena Williams' Open-era record of seven trophies.
But most significant is one statistic.
Every time he's reached the last four, the Serb has lifted the trophy.
And courtesy of Kei Nishikori's withdrawal in their quarter-final, Djokovic is well rested for another championship assault.
"It feels great," said the world No.1.
"This has been my most successful grand slam throughout my career, the first one that I won back in 2008.
"I have a lot of beautiful memories from Rod Laver Arena. Over the past 10 years, I've had plenty of success here."
Djokovic's next challenge on Friday night is Lucas Pouille, the resurgent 28th seed who will be appearing his first major semi-final after thriving under new coach Amelie Mauresmo.
"I always thought he's a great quality player," Djokovic said.
"What he has done this tournament is fantastic. He has won against some top players - of course Milos (Raonic), (Borna) Coric.
"He struggled a little bit with the consistency of his results in the last two years but, with the quality of the tennis that he possesses, he deserves to be definitely at the top 15, maybe top 10 of the world.
"I'm looking forward to a battle. It is his first semi-final at a slam but he has won against Rafa in New York a couple of years ago. He has had some big scalps. He's not afraid to play his best at the biggest stage in sport."
The Frenchman turned to Mauresmo late last year.
Mauresmo, who previously helped two-time women's Australian Open champion Victoria Azarenka to world No.1 and compatriot Marion Bartoli to her surprise 2013 Wimbledon title, had been appointed as France's Davis Cup captain for 2019.
But unhappy with the radical changes to the Davis Cup format after France's loss to Croatia in last year's final, Mauresmo and Pouille linked up instead.
The results have been startling.
Having never won a match in five previous trips to Melbourne Park, Pouille is now two wins away from the title and credits Mauresmo for the transformation.
"She has the right state of mind and knows everything about tennis. It's not about being a woman. It doesn't matter," Pouille said of his new mentor, who has also coached former men's world No.1 Andy Murray.
"You just have to know what you're doing and she does. Men are coaching women, so why not the contrary?
"She's a champion. She's a great coach."
Top-seeded Djokovic or Pouille will play the winner of Thursday night's first semi-final between world No.2 and 2009 Open champion Rafael Nadal or Greek sensation Stefanos Tsitsipas in Sunday's title decider.
