NEW YORK -- Sachia Vickery was 5 1/2 when she told her mother, Paula Liverpool, she was going to be the next Serena Williams. Vickery watched Serena and sister Venus on TV and made tennis her life goal. She even spent a summer with their dad Richard Williams as her coach.

Thirteen years after her pronouncement, Vickery made her U.S. Open debut Tuesday and knocked off Croatia's Mirjana Lucic-Baroni, 6-4, 6-4.

"Surprisingly, I wasn't that nervous. In the first set, I just went out there," Vickery said. "As it got into the second set, I was realizing I could actually win this and I tightened up a bit, which probably didn't help for a few games. I'm just happy I pulled it out."

Liverpool, a paralegal and a flight attendant who ran high school track in her native Guyana, devoted her single motherhood to supporting Vickery and her tennis career. Vickery started playing in public parks and by 12, she was sent to Patrick Mouratoglou's Tennis Acadmey in France.

"[Patrick's] a really good guy," she said. "They really helped my game develop to a really good point. They were looking out for me those three years because I wasn't getting much help and they were there to help me and back me. I'm just really thankful that he let me train there."

Mouratoglou was not the only top level coach Vickery worked with as a child. Richard Williams was impressed enough during his sessions with her that he told the Sarasota Herald-Tribune in 2008 that she was "the next Venus or Serena on the way."

"I used to train with [him] when I was younger and he's a really good mentor," she said. "I see him occasionally because I live in Florida and sometimes I go down there to practice with him, just occasionally, but I haven't seen him in a while."

It was not long before Vickery's training turned into a career. By age 14, she turned pro and started competing in ITF events.

Now 18, Vickery is based at the USTA Training Center in Boca Raton, Fla., with coach Kathy Rinaldi. A victory in this year's USTA Girls' 18s National Championship in San Diego earned Vickery a spot in the U.S. Open draw.

"Honestly, it hasn't sunk in yet," she said after beating Lucic-Baroni. "I still can't believe I won the match. I'm still kind of in shock. I'm sure probably by tomorrow some time, I'll realize I won my first round, but for now, I'm so happy and I'm so excited."

The win will revive the Serena comparisons. "For the longest time she insisted on being called Serena," childhood coach Gerri Braxton told the Herald-Tribune in 2008.

Vickery takes pride in the link to her role model, but she says it is time for her to make her own name. Sachia Vickery is Sacha Vickery.

"It's great to be compared with Serena obviously. She's like the greatest of all-time," Vickery said. "She's the reason I started playing tennis. I should try and make my own mark and come out as Sacha Vickery even though Serena's a great champion. I don't even think I deserve to be mentioned in the same category as her. I'm just going to worry about being me first."

For Serena and Venus, the little girl that their father once raved about now shares the same locker room as they do. The interactions between the Williams sisters and Vickery are much different than they were a few years ago. Serena kept an eye on the Girls' 18s National Championship, knowing that a victory there would send Vickery to the U.S. Open.

"I saw Serena briefly in the locker room and she was congratulating me on winning hard courts," Vickery said. "She noticed and she told me she was following me and my results, so that was the most exciting part so far."

Venus provided a scouting report on Vickery's first-round opponent. Venus defeated Lucic-Baroni her in their two career matches.

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"[Venus] was encouraging me and giving me some pointers about the girl I was playing today, which helped a lot," Vickery said.

Whether Venus' advice helped or not, Vickery, ranked 238 in the world, wowed the Court 7 crowd, and her skill is on the rise.

"My game seems to be coming together a little bit more and I'm getting more confident in the more matches I play," Vickery said. "I think I'm at a point right now I understand where my strengths are and I'm able to use it better than I was before."

That may be bad news for the rest of the tour. Just 18, Vickery has a world of potential remaining. She has already backed much of the Serena comparisons by reaching the U.S. Open at such a young age. Expectations have never proven to be her weakness.

At 5-5, Vickery isn't quite as big as Serena (5-9) or Venus (6-1). That and her calm demeanor might not project an imposing presence, but Vickery is comfortable where she stands -- on the grounds of the USTA Billie Jean King National Tennis Center.

"Being around the players, it just gives me a lot of confidence like I belong here," she said.

One player who may not be surprised by Vickery's ascent is Julia Glushko, who happens to be her next opponent. The 23-year-old Israeli, who knocked off No. 20 seed Nadia Petrova in her first-round match, trained with Vickery at Mouratoglou.

"I know her really well," Vickery said. "She's a really nice girl and we're really good friends, so hopefully we'll have a good match."

Either way, Vickery has reached a checkpoint at age 18. Once self-proclaimed "Serena," she has her first victory on the stage Serena has conquered four times. The talent is present.

Sachia Vickery sent a message Tuesday: Bring on the expectations.

Which of course begs the question. Is she the next Serena?

-- Follow Jeffrey Eisenband on Twitter @JeffEisenband.