But Williams was determined to get home in time to put her daughter to bed, reeling off five successive games to get the job done in straight sets, eventually winning on her sixth match point.
Williams was not the most mobile from the baseline but she was able to dominate from deep, her power enabling her to dictate most of the rallies - the deep forehand cross-court a particularly productive weapon. "Now that I'm not playing doubles in this event, I have the day off, I think that will help".
Sloane Stephens of the United States sits in her chair after losing a set to Donna Vekic of Croatia during the Womens Singles first round match at the Wimbledon Tennis Championships in London, Monday.
The eight-time champion began his title defense in style at the All England Club, brushing aside Dusan Lajovic of Serbia 6-1, 6-3, 6-4 in 79 minutes on Centre Court.
Apart from adjusting to her role "as a working mom", the seven-time champion also had to get used to hearing something "new" as she was addressed as "Mrs Williams" for the first time at the grasscourt major following her marriage to Reddit co-founder Alexis Ohanian past year.
She is competing in her second grand slam since giving birth, having reached the fourth round of the French Open before withdrawing with a pectoral injury ahead of a match against old rival Maria Sharapova.
In other words, Williams was in the mood to gab Sunday at a pre-tournament news conference postponed a day so she could accompany her recently married royal friend, the former Meghan Markle, to watch Prince Harry play polo.
Williams has won 15 matches in a row at Wimbledon, a streak that encompasses titles in 2015 and 2016, although Williams said that hadn't occurred to her until a reporter mentioned it.
Seven-time champion Williams, the 25th seed after having a baby in September, did not have it all her own way against the left-hander's formidable forehand.
After just 20 minutes to complete the first set, Federer went on to fire 35 winners past Lajovic, breaking serve five times, setting up a second round encounter against Lukas Lacko of Slovakia.
It is still hot and humid in Toronto
Low temperatures overnight are expected to be in the high teens to low twenties providing little relief from the heat. Mylene Drouin, the Montreal Regional Director of Public Health, confirmed the deaths were due to heat.
Williams faces Tereza Smitkova or Viktoriya Tomova next.
Rus rolled her eyes at that notion after the match, saying: "I mean, she doesn't start a tournament if she's not prepared".
Williams came back from a set down to win 6-7 (3/7) 6-2 6-1.
Wozniacki arrives at Wimbledon on the back of victory at the Nature Valley International and opened her campaign with a 6-0 6-3 demolition of Varvara Lepchenko. Pliskova ousted Harriet Dart earlier Monday.
She took the first set with a well-timed break at 6-5, with Rus serving to take it to a tie-break. "I've been tested quite a bit, quite frequently out of competition".
"How is it I'm getting tested five times?"
"I don't think I ever actually lost that competitive side".
Last year's semifinalist Magdalena Rybarikova also exited, losing 7-5, 6-3 to Sorana Cirstea of Romania.