Tommy Haas is playing some of the finest tennis of his life, but Novak Djokovic knows that will not be enough if he plays to his best.
The pair close Centre Court today as the second week at Wimbledon gets off with a bang.
Haas will be world number one Djokovic's toughest opponent at the All England Club to date, although the 13th seed is as long as 9/1 for victory with some bookmakers.
The Serbian is not taking the 35-year-old for granted, though.
Djokovic may have won their quarter-final clash at the French Open just a few weeks back, but Haas came out on top at the Miami Masters in March.
"Against Tommy Haas, it's going to be a big challenge for both of us," the top seed said.
"I think it's his most preferred surface. He loves playing on grass.
"He had a few great wins lately. He beat Roger in the finals of Halle last year.
"He played again really well this season on grass. In general, this season he played great.
"I mean, he's 35, 36 years old, and he's been playing very close to the best tennis of his life, in my opinion.
"He's very fit. He doesn't look like a 35-year-old man, for sure. He's full of confidence on the court.
"Look, there's no clear favourite in that match. I need to try to repeat the performance from (the match against Jeremy Chardy).
"If I do so, if I feel this well, I think I have a good chance."
The victor of that clash will face Bernard Tomic or world number six Tomas Berdych in the quarter-finals.
The other ties in that half of the draw see fourth seed David Ferrer take on Ivan Dodig and Andreas Seppi face Juan Martin Del Potro.
Most of the home interest today will focus on Andy Murray, who takes on in-form Mikhail Youzhny after the Russian came through Saturday's clash with Viktor Troicki.
It promises to be a fine day of tennis and British fans will be keeping half an eye on the clash between Fernando Verdasco and Kenny De Schepper, with the winner facing Murray should he overcame Youzhny.
In the semi-finals, the highest-ranked player the Briton could face is Jerzy Janowicz.
The Polish 24th seed takes on Austria's Jurgen Melzer, with the winner facing either Lukasz Kubot or Adrian Mannarino in the quarter-finals.