And he watched it again and again, taking note of Federer's quickness, net game, serve, variety of tactics and, above all, his composure.
Novak Djokovic won his battle to be promoted to Centre Court billing for Wednesday's quarter-finals, forcing eight-time champion Roger Federer off the sport's most famous arena for the first time in three years.
"I guess there are other factors that play in".
Federer and Nadal are favorites to meet in Sunday's final - 10 years after their epic 2008 showdown - but Wilander believes Del Potro could throw a spanner in the works.
That's a decision that should please Djokovic, who told Serbian media on Monday that he was unhappy about playing all but one of his matches this year away from Centre Court.
Since seeds were introduced in the 1920s, it's the first time none of the top-10 have reached the women's quarterfinals at Wimbledon.
Victory for Nadal over his fellow left-hander would take him into a 35th Grand Slam quarterfinal.
Bertens and Pliskova had reached the fourth round at Wimbledon for the first time.
Goerges will face seven-time champion Serena Williams in the semifinals on Thursday. As you have already guessed, it's Wimbledon time.
A battle of the big servers which is likely to see plenty of baseline rallies and not much court-craft.
The 36-year-old is more renowned for defending tennis titles than forward defences, but this dexterous left-handed shot displayed his innate sporting talent.
Bertens, who was contemplating retirement past year after losing her enthusiasm for the sport, is the first Dutch woman to reach the Wimbledon quarterfinals since Michaella Krajicek in 2007.
Beaten by Serena in the 2016 final, Kerber takes on Russian 14th seed Daria Kasatkina, a 6-7 (6/8), 6-3, 6-2 victor against Belgian world number 47 Alison Van Uytvanck. It's normal that I lost here, too.
Three times he has been scheduled last on court, putting him at risk of falling victim to fading light with the burden of having to return the following day.
It's that time of the year when Tennis fans across the globe hook themselves to their TV sets and can not afford to miss even a second.
Later Monday, two-time champion Rafael Nadal attempts to make the quarterfinals for the first time since he finished runner-up in 2011.
(12) Jelena Ostapenko bt. "It will stay this year, it will stay next year", said All England Club chief executive Richard Lewis.
She took advantage of the 14th-seeded Kasatkina's 31 unforced errors, including seven double-faults.
He looked flat as he was broken to trail 1-3 but he clawed his way back to lead 5-4 with his serve to come.
Williams dropped just four games as she dispatched Rodina, hitting 30 winners in the process compared to her opponent's five.
Del Potro is in his first quarter-final at the tournament since 2013 when he reached the semi-final.