CiCi Bellis
CiCi BellisUS Open website

America's new teen sensation CiCi Bellis defeated no.12 seed Dominika Cibulkova to become the youngest winner at US Open in 18 years. 

Bellis saw off the 2014 Australian Open runner-up 6-1, 4-6, 6-4, to pull off one of the biggest upsets in the tournament's history. The teen is now the youngest player to win a US Open match since 1996, after Anna Kournikova.

"Believing was the No. 1 thing that I had to do today," Bellis stressed. "I went into the match thinking it was going to be such a great experience."

"It gave me so much energy," she said about the crowd. "I love that. I love when people watch me."

The young American said she never expected she would share courts with some of tennis' all-time greats, during the pratice sessions at the US Open.

"It's crazy to think I'm actually here right now with all these other people. I mean, I never thought I would be practicing or sharing a court with, you know, a player I watch on TV. I mean, it's crazy. But I love it."

Bellis won the USTA Girls 18's National Championships that gave her a wildcard to the US Open. She had also won Les Petits As in 2013, a prestigious junior tournament in France, and finished runner-up in the French Open juniors doubles.

Bellis has set up some rules for her father Gordon for her tournaments.

"I'm told I cannot sigh and I cannot move or say anything (because) that distracts her, so I just have to sit there like a Sphinx and just smile and pray," Gordon said.

Cibulkova said she had no clue about Bellis' game and definitely underestimated the teenager.

"I didn't expect her to play so aggressive today. I thought she's kind of a player who's just putting the ball back and running around," the 25-year-old admitted. "That didn't happen today. She was really aggressive on the court and that maybe surprised me in the first set."

Bellis will play Zarina Diyas of Kazakhstan in a second-round on Thursday.

Meanwhile, Serena Williams ousted Taylor Townsend 6-3, 6-1 win to reach the second round. The world no.1 got past her fellow American in less than one hour.

Williams made only eight unforced errors in her quest to become the first woman to win the US Open three years consecutively since Chris Evert, who sealed four straight titles from 1975-78.

Williams has won five US Open titles overall, which is part of the 17 Grand Slams she has in her kitty.

18-year-old Townsend, who Williams regards as "the future of American tennis", was given a wild card into the draw but was thrashed by the number 1 seed.

"I love coming out to play here. This was the first slam I won and I love to come back. I never want it to stop," the 33-year-old said.

However, Williams has struggled in Grand Slams this year, failing to get past the fourth round at the Australian Open, French Open and Wimbledon.

Meanwhile, Wimbledon winner Petra Kvitova beat Kristina Mladenovic 6-1, 6-0 to make it to the next round, while Eugenie Bouchard thumped Olga Govortsova 6-2, 6-1.

Also, Ana Ivanovic won comfortably against Alison Riske 6-3, 6-0, while Sam Stosur beat Laura Davis 6-1, 6-4.