(CNN) The two tennis legends have won 43 grand slam singles titles between them and are considered by many to be the greatest of all time.
But in careers lasting over 20 years Roger Federer and Serena Williams have never faced each other in a competitive match, until their eagerly-anticipated New Year's Day clash at the Hopman Cup in Perth.
Williams came safely through her first official outing since her controversial US Open final loss with a straight sets win over Maria Sakkari of Greece Monday.
Despite a 7-6 6-2 win for Williams, the United States fell to a 2-1 loss to Greece, making Tuesday's clash with Federer's Switzerland a must win for the six-time champions in the mixed team competition.
The greats will oppose each other in a mixed doubles match where Williams will pair with US teammate Frances Tiafoe, with Federer partnering Belinda Bencic.
Sharing the same court as Federer will be "like a dream come," said the 37-year-old Williams after her comeback win.
"I have been looking forward to it, this is so cool."
Organizers would have been holding their breath as Williams, playing with taping on her ankles, received treatment on her left ankle at the end of a lengthy first set, but she insisted it was merely caused by discomfort with her shoes.
Sakkari had served for the opening set, but wasted her opportunity and once her illustrious opponent had won the tiebreak 7-3 it was one-way traffic as Williams eased to victory in one hour 44 minutes.
"I was making a lot of errors and I'm like 'it's okay, it's your first match, it'll get better'," she said.
"It's never easy (the first match), there are lot of errors that are going to be made and I think we both did pretty good."
The hard-fought victory leveled the tie at 1-1 after Tiafoe had lost his singles to Stefanos Tsitsipas, but ultimately it was the Greeks pair who prevailed, winning the deciding mixed doubles 4-1 1-4 4-2.
Williams is warming up for next month's Australian Open where she is hoping to equal Margaret Court's all-time grand slam titles record of 24.
September's US Open saw her lose in the final to Japan's Naomi Osaka, the match overshadowed by Williams' on-court fracas with match umpire Carlos Ramos, calling the official a "liar" and a "thief" on the way to 6-2 6-4 defeat.
The US Open was also a shattering disappointment for Federer, wilting in the intense New Year heat to lose his last 16 clash with Australian John Millman.
The veteran Swiss maestro looked in fine shape as he dispatched Cameron Norrie of Great Britain Sunday in straight sets as defending champion Switzerland won its opener in the Hopman Cup 3-0.
He is looking forward to what some commentators are describing as the "Battle of the Sexes", a reference to the famous 1973 clash between Billie-Jean King and former Wimbledon champion Bobby Riggs.
Hype maybe, but Federer is intrigued to be finally facing up to his fellow 37-year-old, the pair having been at the top of the tennis tree since the early part of the century.
"It's very exciting for us," he said.
"I admire everything she has done on and off the court. I have always thought what it was like to return that serve and go head to head with her," he added.
Meanwhile, there was also a return to competitive action Monday for Russia's Maria Sharapova, the five-time grand slam champion beating Switzerland's Timea Bacsinszky in straight sets, 6-2 7-6, at a WTA Tour event in China.
Sharapova was greeted by adoring crowds at the Shenzhen OIpen and did not disappoint with a typically dogged display against a former top 10 player.
'It's been a few months since I was out playing competitively," she said. "I think it was great practice for me," she added.
Sharapova will be looking to improve on her indifferent form at the grand slams since her return from a doping ban in April 2017 at next month's opening grand slam of 2019, which starts on January 14.