“I didn’t get much sleep last night; I was up until 2 a.m. last night just thinking about it,” the 20-year-old Joint said.
“The start was very nerve-wracking. Trying to close out the match, she definitely raised her level.”
Williams announced her shock return to the sport earlier this month and had played two doubles matches ahead of Wimbledon.
The 23-time Grand Slam champion became the second-oldest player to feature in the Wimbledon women’s singles in the Open era, after nine-time champion Martina Navratilova, who reached the second round aged 47 in 2004.
Williams was given a rousing reception when she stepped on to court, but the crowd could not push her to a famous victory, despite rapturous celebrations when she won the second set.
The American legend won the last of her seven Wimbledon titles a decade ago, and her last Grand Slam triumph came at the 2017 Australian Open, when she was pregnant with her first child.
Joint, who had lost 13 of her last 14 matches and slipped to 87th in the WTA rankings, rediscovered the game which had taken her into the top 30 as recently as February.
She will next face Filipina rising star Alexandra Eala after the 29th seed dropped just three games in her first-ever Wimbledon win over Renata Zarazua.
Serena will turn her attention to her bid to win a seventh Wimbledon women’s doubles title alongside 46-year-old sister Venus.