The 37-year-old tennis star has been friends with the former actress - who was known as Meghan Markle before marrying Prince Harry last year - for several years and took on the task of planning her baby shower back in February for the tot she's expecting any day now, and has now revealed the party was a lot more pressure than she'd first thought.
Speaking to Business of Fashion, she said: "Planning something like that takes a lot of effort. I'm a perfectionist, so I'm like, 'Let's make it perfect.'"
Serena - who has a 19-month-old daughter of her own named Alexis Olympia - threw Meghan's shower at The Mark Hotel, where guests were treated to a flower-arranging class and plenty of delicious food.
The sporting superstar invited the likes of Amal Clooney, Gayle King, Jessica Mulroney, Misha Nonoo, and Abigail Spencer to the event.
Meanwhile, Serena recently insisted the Duchess will make a great mother when her first child is born in the near future.
She said: "She'll be the best mom, for sure."
And the star even shared some of her tips on coping with parenthood for the first time, saying she had to learn to "go with the flow" and adapt to living day-to-day without too much planning to avoid causing unnecessary stress.
Serena added: "Accept mistakes and don't expect to be perfect. We put so much pressure on ourselves.
"I had all those high expectations and what I was going to do and then I had what I was going to do.
"I was gonna recover and I was gonna be great, and this is a time that everything is not going to go as planned.
"My whole life is so planned and this is the one time where it wasn't. You just gotta go with the flow."