Federer, the defending champion and seeking a 21st major, marked the start of his 20th successive Wimbledon with a new look and a comfortable 6-1, 6-3, 6-4 win over Serbia's Dusan Lajovic.
A Williams' spokeswoman later reached out to Deadspin and called the test "invasive and targeted".
Athletes on USADA's testing list are required to inform the agency of their whereabouts at all times of year, and they must make themselves available for a 60-minute window each day during which a collector may arrive. "You guys are making me miss her".
"I actually thought the article was interesting, to be honest, because I never knew that I was tested so much more than everyone else", said Williams, who is in search of a record-tying 24th Grand Slam singles title.
"You only get three missed tests". For me, it's a little frustrating.
Federer claimed he has been tested seven times during the past month - including at tournaments in Stuttgart and Halle - and he pointed out the remarkable variation between the amounts of tests carried out from place to place.
"It's really disappointing, shocking". Something that I would normally be okay with, normally have, 'Oh, this is this.' It's just getting all back to the hang of things, getting used to different circumstances.
The incident was made public after WTA chief Steve Simon was overheard leaving a message on Williams' answerphone at an airport.
Serena Williams returns after missing Wimbledon past year while she was pregnant. "I often find the less I serve, the better I serve, which is totally weird". "But I am a little bit shocked at how much I nearly want that pressure". What I want to know is everyone is getting tested, that we are really working to keep this sport clean.
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She got it wrong at last month's French Open, she acknowledged, in trying to play both singles and doubles.
"I don't at all feel that way".
Serena Williams has thanked Wimbledon chiefs for giving her the controversial seeding that divided the tennis world ahead of the grass-court Grand Slam.
But at the same tournament where he played what proved to be his last match of 2017, the 33-year-old was rejuvenated. "I thought, "Hey, I have this wonderful child, I have all these Grand Slams, this is all super bonus", and it is".
The 25th seed had to battle from a break down in the second set but went on to win five games in a row to set up a second-round encounter against either Tereza Smitkova or Viktoriya Tomova. I'm okay with that. I mentioned many times in Dubai I've hardly ever been tested, which has been quite disappointing. That's all I care about. It's just about being equal and not centring one person out. "Just test everyone equally".
In the American's absence, Spain's Garbine Muguruza won Wimbledon for the first time with a final victory over Serena's sister Venus.
"We'll always have that footage of her. Where I live in Switzerland, the tester lives in the same village, so it's very convenient!" he said.
That move sparked mixed feelings from the former world number one's fellow players, with some supporting the decision and other grumbling about unfair treatment.
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