PLANTATION, Fla. — The tennis coach Kathy Rinaldi settled into her folding beach chair near the court, out of the sun’s range but close enough for her encouragement to be heard by her teenage pupil, Taylor Townsend. A few feet away, a woman, dressed from visor to sneakers in tennis whites, was speaking on her phone: “I’m getting ready to watch Taylor Townsend. She’s the girl who looks like Serena.”

The setting was a December junior tournament, the Orange Bowl International Championship, sanctioned by the United States Tennis Association and the International Tennis Federation, here at Veltri Tennis Center outside Fort Lauderdale. The 16-year-old Townsend was competing in the girls 18-and-under division for the final time after declaring her intention to play for pay starting in January.

Townsend enters the professional ranks with credentials that unfurl like a red carpet: the 2012 Australian Open junior singles and doubles titles and the junior doubles title at this year’s Wimbledon and United States Open. She is the first American to hold the No. 1 year-end world ranking for junior girls since Gretchen Rush in 1982.

Because she is black and has a sturdy 5-foot-6 physique and strong ground strokes, Townsend often draws comparisons to Serena Williams, a 15-time major singles champion. Townsend said she was flattered to be mentioned in the same breath as one of the greatest players in the game’s history. But occasionally, the surface comparisons cut deep.