Despite being a spectator, Pam Shriver looked flushed the other day as she left Show Court 3 at the Australian Open. "That was the real deal," said Shriver, the former United States star, as she touched her open palm rapidly to her chest to demonstrate her racing pulse.
"You don't have a serve like that at 17 years old. The way she got out of that love-40 game. The easy power. The big forehand. It's exciting. I haven't felt this for 15 years."
The real deal in question was Madison Keys, still only 17 at a time when true teenage prodigies have become scarcer on the Grand Slam grounds. But Keys, a tall and powerfully built player from Florida by way of Illinois, has been imposing herself on her elders with a newfound regularity this season.
Keys, long considered one of the top US prospects, is no Grand Slam debutante. She won a round at the 2011 US Open at age 16 and lost in the first round of the Australian Open last year as a wild card. But her game, brimming with power and promise, has reached a new level of maturity and menace.
Keys reached the third round before bowing out but experts didn't fail to notice her talent.
"She can produce power from pretty much anywhere on the court, but her serve is, I think, her biggest weapon," said Juan Todero, her coach at the US Tennis Association.
Shriver, a former US Open singles finalist and serial doubles champion, suggested that by the end of the year Keys might have the second-best serve in the women's game after Serena Williams.
Lindsay Davenport, an American who was once ranked No 1, said in a Twitter message: "Really fun watching Keys play. Regardless of how this tourney plays out, incredible potential."
Asked how Davenport's faith made her feel, Keys said: "I mean, it makes me happy. You know, I think I've been working really hard. I think it's starting to show."
But perhaps this is the right time to take a collective deep breath and let the 105th-ranked Keys generate a few more upsets and pressure aces down the T before sprinting to conclusions and trophy presentations.
"Listen, I still see some ups and downs for the next 18 months, but I think by the time she's 20 years old, she's going to have a really good package," said her agent Max Eisenbud, who also represents Maria Sharapova and Li Na.
"So hopefully Sloane can take all the attention and let Madison stay under the radar."
Sloane is Sloane Stephens, another talented American teen.
Keys is clearly part of a youth movement this year. There were three teenagers in the second round of the Australian Open in 2012. This year, there were 11, which would seem to run counter to the idea that the modern women's game has become too physically demanding for youngsters to make an impact.
"There are definitely some players coming up, I agree," veteran coach Sven Groeneveld said. "But for the moment, they have made a move but they have not made a mark." Opportunities, however daunting, abound.
Donna Vekic of Croatia, the youngest singles player in the tournament at 16, turned heads last year by reaching the final of the WTA event in Tashkent, Uzbekistan, and she turned some more in Melbourne by winning her first Grand Slam match, defeating Czech veteran Andrea Hlavackova, 6-1, 6-2 before Caroline Wozniacki halted her.
Vekic trains regularly in Britain with David Felgate, the former coach of British star Tim Henman. She has a proper English accent as well as elastic strokes that bring to mind the current world No 1, Victoria Azarenka. British reporters were investigating whether she had any interest in switching allegiances. Answer for now: a polite no.
"I'm very happy playing for Croatia, and us Croatians have a big Croatian heart, you know, fighting on court for your country," Vekic said.
The consensus is that it is now all but impossible for a girl to achieve the same sort of consistent, early success at this level that players like Steffi Graf, Monica Seles, Jennifer Capriati and Martina Hingis managed in the 1980s and 1990s. Capriati reached her first Grand Slam semifinal at 14, Seles at 15 and Graf at 16. Hingis won her first Grand Slam title and reached No 1 at age 16.
The WTA age eligibility rule, put in place to protect girls from physical and psychological pressures, has also played a role in limiting the impact of the youngsters. The rule, which has its critics, restricts players' tournament play and the number of wild cards they can receive until they turn 18.
"I personally think that the rule is hurting the star power of the game," said Eisenbud, who added he was ultimately in favour of the rule because it extended players' careers.
Keys will turn 18 on February 17 and will play the rest of the 2013 season without restrictions.
"The key to her recent success, in my opinion, is that she has taken more ownership over her game, realising what she needs to do to play good tennis, not great tennis," Adam Peterson, the USTA coach who was once Keys' primary coach, said in an email message.
"Before, she tried to play great tennis all the time, forcing things. She's playing much more within herself now and allowing her physical advantage to come through. She's gotten a lot fitter and stronger over the past 12 months."
Chris Evert, who helped coach Keys in the early years at her academy in Boca Raton, is convinced the women's game has changed definitively.
"We're not going to see any more 15-year-old phenoms," Evert said. "I beat Margaret Court when I was 15. Monica Seles beat me when she was 15, and then Steffi Graf beat me when she was 15. And Martina Hingis was beating the No 1 players in the world when she was 15. No more, no more. You're just not going to see it anymore."
It was pointed out that Keys had beaten Serena Williams, 5-1, during a World Team Tennis match when Keys was 14.
"No, no, no, that doesn't count," Evert said. "That's funny, though."