As Williams searches for grand slam title number 23 -- the one that will cement her as the greatest female player of all time -- Keys is being backed to deliver her first in 2017.
And when Serena hangs up her racket, countrywoman Keys could be in the frame to emerge as her successor -- not only according to Williams -- but also to a pair of legends with an incredible 36 majors between them.
"She's harnessing her power on both wings -- so much power -- and her serve is comparable to Serena Williams," Chris Evert told CNN's Open Court show.
"I think the reason why she's here to stay and she's the real thing is because she's taken baby steps."
The American star secured 18 major titles in her glittering career, the same figure as Czech-born Martina Navratilova, and both agree that 2017 could be the 21-year-old's breakthrough year.
Top 10 breakthrough
Keys has steadily built momentum during 2016.
The Illinois-born star secured her second WTA Tour title at Eastbourne in June, and subsequently became the first American woman to break into the world's top 10, since -- you guessed it -- Serena back in 1999.
After Keys at No. 7 comes Venus Williams at 17, the player that compelled her to get involved in the sport, and after that is Sloane Stephens down in 36th.
Keys' late run of form saw her make the final four in both Beijing, China, and Linz, Austria, and secured her a place at the season-ending WTA Finals for the first time.
"She didn't come on really strong like Genie Bouchard or Garbine Muguruza -- she hasn't been ready mentally," Evert explained. "The mental and emotional side is catching up with the physical side."
Navratilova agrees: "She's taming the power and she's picking the spots better when she's going for her shots. That match she played (against Dominika Cibulkova at the WTA Finals) ... I was really impressed.
"The younger generation is coming together nicely and we've been hoping Madison Keys would have a better year than last year."
Williams is well aware that Keys has the potential to be her protege.
The pair have met on three occasions, most recently in the final of the Italian Open in Rome back in May.
But even after their first encounter, at the Australian Open semifinal of 2015, Williams was glowing with praise for her vanquished opponent.
After a 7-6 6-2 victory that paved the way for a 20th grand slam success, Williams told the crowd in Melbourne: "It was an honor for me to play someone who will be No. 1 in the future."
Serena's quest for 23
Before Serena hands the baton on to Keys, she's got some serious business to attend to.
The 35-year-old's victory at Wimbledon this year -- her only grand slam title of 2016 -- pulled her level with Steffi Graf's record 22 titles in the Open era.
But a fairytale US Open campaign did not materialize. After succumbing to Karolina Pliskova in the semifinals, Williams lost her world No. 1 ranking to the tournament's eventual winner Angelique Kerber.
That meant she and Graf could not be separated on another count, both having spent 186 consecutive weeks occupying top spot.
With her playing schedule getting ever lighter as she prioritizes the slams, and with persistent injuries niggling at her, there have been question marks as to whether Serena will get over the line.
But Navratilova and Evert are confident she'll scale her Everest.
"I think she definitely has one more if not two more grand slams left in her, especially Wimbledon where the surface seems to suit her power," Evert said.
Navratilova concurs that Wimbledon might be her best chance of eclipsing Graf's haul, which has stood as the benchmark since her last triumph at the French Open in 1999.
In fact, she thinks only injury can prevent Williams from landing her eighth Wimbledon crown, to surpass Graf's seven.
"If Serena stays healthy it's almost impossible for someone to beat her on the grass," Navratilova said. "That's her best chance at it. I think she will be motivated -- she definitely wants that record.
"If anyone can do it, obviously, Serena Williams can. The biggest question mark is her motivation but an even bigger one would be her health. If she can stay healthy and get her shoulder organized, you can not bet against her to win one or maybe two slams."