Williams was the WTA's top-ranked player for 186 consecutive weeks, equaling Steffi Graf's Open era record. Djokovic occupied the ATP World Tour throne for 122 consecutive weeks. Collectively, that's nearly six straight years of dominance.
The year-end obituaries of the fallen No. 2-ranked players, however, sounded a bit shrill.
As 2017 rapidly approaches, we can report that Williams -- now a doddering 35 -- and the 29-year-old Djokovic are still breathing. In fact, it wouldn't be a stretch to imagine them winning multiple Slams and reclaiming their No. 1 rankings.
Amid all the hype and talk of change, it's easy to forget that Djokovic won the first two majors of the season and made the final of the fourth; Williams lost to Kerber in the final of the Australian Open and beat her in the Wimbledon final.
In retrospect, it's now clear Serena spoiled us with a late-career surge that has no historic parallel. After turning 30, following the 2011 US Open, she won nine of the next 20 Grand Slam singles titles -- dominating women's tennis over a five-year span in spectacular fashion.
She and Djokovic still have their supporters.
"It's Jan. 30, the Monday after the Australian Open ends," said Brad Gilbert, who coached Andy Murray, Andre Agassi and Andy Roddick. "And you tell me that [Serena/Djokovic] double happened. No, I wouldn't be surprised -- at all.
"Djoker has won six of those titles. Serena's like a stock -- how do you predict it? The fact she's played as little as she has -- she's 35, and she's probably the betting favorite. Sort of like Tom Brady and the Patriots. Don't focus on the age; look at the history."
Both Djokovic and Williams struggled with injuries, which led to diminished confidence -- their signature weapon in recent years.
Heading into this year's US Open, Williams was still a favorite, and with a title, would have strung together another excellent year. Instead she got beaten by ascendant Karolina Pliskova in the semifinals.
"I wasn't able to move the way I wanted to move," Williams told the media afterward. "When you're injured, you're thinking of other things when you should be just playing and thinking of your shots. My mind was just a little bit everywhere."
So was her season. There were surprisingly early losses in the Rio Olympics in singles and, with sister Venus, doubles. Serena finished with two titles (Wimbledon and Rome) and played only 44 matches, her lowest totals in five years. And, for the second consecutive year, she shut her season down after the US Open.
Her coach, Patrick Mouratoglou, was moved to call it "a very bad season."
Williams, who was dogged by shoulder and knee issues, literally limped away from the year.
Djokovic nursed a nagging arm injury and, after winning the French Open to complete his career Grand Slam, tailed off drastically. After losing to Murray in the final of the ATP year-end event, Djokovic looked and sounded weary.
"Right now," he said to the media, "the goal is just to rest a little bit. It's been a long season, a very nice year, a lot to reflect on, a lot to take in. It's time to leave the racket aside for a little bit, just recover."
There will be no recovery for six-time Grand Slam champion Boris Becker, the coach who was the most notable collateral damage after Djokovic's second-half swoon. After three years with Djokovic, Becker was terminated at the end of the season.
Because they're getting a bit older, both Djokovic and Williams will be playing in 2017 with an enormous sense of urgency. It's suddenly a shrinking universe, with all kinds of younger players -- Milos Raonic, Kei Nishikori, Nick Kyrgios, Simona Halep, Pliskova and Madison Keys -- all looking for their first Slam win.
Nearing 30, Djokovic has crossed that line of demarcation for male tennis players. Roger Federer, Pete Sampras and Rafael Nadal, who have won a total of 45 majors, collected only two among them after their 29th birthdays.
Djokovic, with 12 Grand Slam singles titles, needs two to equal Sampras and Nadal and five to catch Federer. Williams is tied with Graf with 22 major titles, two behind all-time leader Margaret Smith Court.
What must Serena and Djokovic do to successfully hit the reset button?
Pam Shriver, and ESPN analyst who won 21 Grand Slam doubles titles, said they need to make an immediate impression.
"I think they have to play well in Australia -- maybe not win it but go deep in the draw," she said. "For their own confidence and also sending a message to rest of the field. I think it's going to be easier for Djokovic than Serena. I don't have lot of confidence in this mid-30s-take-four-months-off thing. I hope she can prove me wrong. Until then, I am skeptical.
"I think they'll both win majors; one of them will win more than one. The current No. 1s, Kerber and Murray, are in it to win it for the year. On the men's side, I think it will be the most unpredictable year since 2003 going back to Federer's first Slam."