Or was it the court?
Federer took the first two sets but Anderson showed wonderful resolve to fight back and win the third and fourth set.
Top seed Federer had a match point in the 10th game of the third set but made a hash of a backhand and almost two hours later he trudged off a beaten man.
Nadal has a far superior head-to-head record than Federer, and if he ends up winning more majors then it would be game, set, and match when it comes to the GOAT status.
And he didn't stop there.
Man faces hate crime charges over racist Puerto Rico shirt rant
The officer was put on desk duty while officials investigated the incident, but he resigned this week. Trybus is scheduled for his first court appearance August 1, said the Cook County Circuit Court.
It was Federer who caved under the fifth-set pressure with a double-fault and a net error to concede the crucial break before Anderson served out his victory in a four-hour and 14-minute marathon.
He consistently outfought Federer from the baseline, leading to him claim the only break point of the fourth set and take the match into a decider.
Kevin Anderson became the first man to break Federer during the tournament at the start of the second set of their quarterfinal.
Djokovic got his wish to play in the main stadium, and he showed that he might completely be back from right elbow troubles that lasted more than a year until he finally had surgery in February. "It's one of those average days you have to try to win the match, and I just couldn't get it done today".
If Nadal wins Wimbledon and retains his US Open title later in the year, there will only be one major separating him from his old foe Federer.
The Japanese remained in control and served it out to level the match and he appeared in the ascendancy as, after saving a break point, he then raced to a 0-40 lead on Djokovic's next service game. "I was in the flow of the match", eighth seed Anderson said. At the same time, because he's such a big player, has so much firepower, you just can't be too patient. I couldn't really get the rallies going the way I wanted to, especially 1-2 punch wasn't working at all.
Sparks fly in Federal Bureau of Investigation agent's Trump testimony
If you have a problem with this policy, you should take it up with the Federal Bureau of Investigation - not badger Mr. They would not tolerate any improper behavior in me any more than I would tolerate it in them.
"I think I was sort of on the border of actually going on to Australia (in 2017)". With Federer serving for the match at 5-3, 40-15, he hit a wide serve that Djokovic slapped back recklessly, nearly carelessly, for a victor. He could potentially win a set and if he can win a set he could win two sets.
Nadal, four years Federer's junior, is the only realistic rival Federer has to the coveted GOAT status. Djokovic, a 12-time major champion, had not reached the final four of a Grand Slam event since the 2016 US Open. "I feel like I did some good business in the past here already".
Novak Djokovic's clash with Kei Nishikori and Rafael Nadal's duel with Juan Martin del Potro share the Centre Court limelight. "I've actually been a little bit more aggressive this tournament in terms of some of the strength I've done on the off days, which I think has been beneficial", he said.
"I'm not quite sure what to say right now but down two sets, I really just tried my best to keep fighting", Anderson told the BBC in his post-match interview.
"Well, maybe wasn't my best, but I thought I was playing good enough", said Nishikori.
Anderson v Isner will be played at Centre Court, of course, a spot Federer knows well.
Trump visit: 'Baby Donald' is grounded at Turnberry
Embassy in London , which advised Americans in the country to "keep a low profile" in case the demonstrations turn violent. Anti-Trump protesters lined the roadway leading to the palace near Oxford - but it's unlikely the Trumps even saw them.