She jumped and raised her left arm, smashing the ball back at Williams, who watched it zip past her in disbelief.
"Come on!" she screeched in excitement while pumping her fist and running up and down the white baseline.
Townsend beat Williams for three straight games in their set before Williams was subbed for Anastasia Rodionova. Townsend finished the game giving up three points total, subsequently leaving the court and slapping hands with Hall of Famer Billie Jean King along the bench.
For 15 minutes, the words of an adolescent became a nightmare for the 34-year old icon. Townsend showed she belonged.
"It's an honor just to be able to play her," Townsend said before her 5-0 win over Williams and Rodionova.
"I remember the final when she played Serena, and there was so much tension. Growing up, I played with my sister, and we always wanted to re-enact that. I always said that I was going to be better than the Williams sisters. I didn't know how or when it was going to happen or how I was going to get there, but I believed it. The fact that this moment is finally here, it's a pleasure."
The Freedoms crushed the Kastles, 22-15, in front of a small crowd. Coached by Episcopal Academy grad Josh Cohen and owned by King, the Freedoms are in their 15th season with a loaded roster. Townsend, 18, was a late addition to that roster, joining this month to replace her friend Vicky Duval, who was just diagnosed with Hodgkin's lymphoma. Townsend was the first American to hold the No. 1 year-end world ranking for junior girls since 1982.
After redeeming herself by teaming with Rodionova in a 5-3 win in women's doubles, Williams brought the spotlight back her way. The seven-time Grand Slam singles champion and four-time Olympic gold medalist (including three in doubles) said she was excited to play again in Philly, as well as in the 2016 Olympics in Brazil.
"Having played for the Freedoms before playing for the Kastles, this place feels like home," Williams said. "At this point, I'm improving. I'm making my way back after unforeseen circumstances, and I'm moving forward and playing some of my best tennis since 2012. Obviously, what I look most forward to is the Olympics. I'm trying to bring some gold back to the U.S."
Williams said that she was healthy for the match with Townsend and that the reason for her off game was that she "just missed." Williams did say the future is bright for Townsend.
Townsend, who has waited for a moment like this since she was 12, said it was finally starting to sink in on whom she beat.
"It's big for me," Townsend said. "I didn't really focus on the fact that I was playing Venus Williams. I stayed within myself and within my boundaries. But at the same time, this is huge."
On Twitter: @TylerRickyTynes