Naomi Osaka had not yet celebrated her second birthday when Serena Williams celebrated winning the 1999 US Open, the first of her 23 Grand Slam singles titles. Now aged 20, the Japanese No. 1 will be living out a dream when she takes on her childhood idol in Saturday’s US Open women’s singles final.

Despite their 16-year age difference, the two share a lot in common, even beyond their big-hitting games and fearlessness on court from a young age. Serena powered to that '99 US Open title at 17 years old; Osaka is one win away from claiming her first Slam at 20. Heavily influenced by Richard Williams, who taught his daughters on public courts in California, Osaka's Haitian father, Leonard Francois, trained both her and her sister, Mari, on public courts in New York. (Born in her namesake city in Japan, Osaka and her family moved to the U.S. when she was 3). 

"For me, one of the main things was that when I was practicing with my dad, if my sister wasn't there, I don't think I would have made it," Osaka said in a US Open press conference following her semifinal victory. "I think maybe [Serena and I] both have this really big sister connection."

Throughout her childhood, Osaka and her sister paid many visits to the US Open to watch Serena. As they sat in the upper deck, Osaka could never get close enough to snag an autograph. But better than an autograph, Osaka booked a meeting with her hero at the Miami Open earlier this year, their first and only career meeting to date.

It was one of the draw's most anticipated first-round matches: a titan of American tennis facing one of the game's rising stars. Serena had the weight of her 20-year career behind her, while Osaka was riding her own wave; just three days prior, she won her first WTA title in Indian Wells, one of the tour’s biggest events outside the Grand Slams. Her ranking had shot up 22 places, to No. 22. She was on a roll.

In the end, Osaka pulled off the "upset," 6-3, 6-2. She was very subdued in her celebration, not unlike the way Serena conducted herself after defeating her sister in the third round at this US Open. A subtle look to her box and an understated bow in the form of a head nod towards Serena capped a comprehensive victory. The result capped a run of eight matches during which Osaka defeated four current or former WTA No. 1s, also including Maria Sharpova, Karolina Pliskova, and Simona Halep. 

"I don't know if anybody knows this, but Serena is my favorite player," Osaka said in her on-court, post-match interview. "Just playing against her is a dream for me. I'm very grateful that I was able to play her, and it's even better that I was able to win."

For Serena, it was just her second tournament, and fourth match, back from maternity leave. Both she and Osaka know things will be very different come Saturday at 4 p.m.

Serena is dangerously close to her pre-pregnancy best, when she reigned as the world No. 1 for a combined total of 319 weeks. But Osaka is also playing the best tennis of her young career. She is guaranteed to rise to a career-high No. 12 in the next edition of the WTA rankings, with a place in the Top 10 beckoning should she claim the title. Judging by her semifinal performance -- a 6-2, 6-4 thumping of 2017 finalist Madison Keys -- it may not be long until Osaka can lay claim to the No.1 spot herself.

Following her semifinal victory, she was asked how she summoned the mental strength to save all 13 break points she faced in the match.

"This is going to sound really bad, but I was just thinking, I really want to play Serena." Asked if she had a message for her final opponent, Osaka said, through a fit of laughter, "I love you."  

Looking ahead to the final, Osaka described the matchup as “surreal,” adding that she’s “very hyped for it.” But, showing wisdom beyond her age, she remains level-headed.

"At the same time I feel like even though I should enjoy this moment, I should still think of it as another match. Yeah, I shouldn't really think of her as my idol. I should just try to play her as an opponent."

So yes, Saturday’s final will be a dream for Osaka. But in her dreams, how did that match play out?

"You already know," she said with a smile. "I don’t dream to lose."