By Simon Cambers
MELBOURNE (Reuters) - For American tennis, it seems that when one door closes, another opens.
The retirement of Andy Roddick, illness of Mardy Fish and injury to John Isner meant that Sam Querrey is the only American to be seeded on the men's side at the Australian Open.
But in the women's event, four American women including the Williams sisters are seeded, six have made the second round and 10 began the tournament ranked in the top 100.
With Madison Keys making it through to round two, the Americans are scheduled to have 11 in the top 100, their best representation since 2007.
"It's a big plus for American tennis to have so many," rising U.S. player and 21st seed Varvara Lepchenko told reporters after her 6-4 6-1 win over Polona Hercog of Slovenia on Tuesday.
"We're all trying to compete hard and do our best and improve out there and do as much as we can.
"All the girls are looking up at each other and saying, ‘I'd been playing with her, I'd been competing with her, I've been playing on the same level,' so we push each other and it gives a lot of confidence to others and everybody improves."
When Chris Evert and Martina Navratilova were winning most of the grand slam titles in the early 1980s, the U.S. dominated women's tennis.
The arrival of Steffi Graf and Monica Seles balanced affairs but Lindsay Davenport and Jennifer Capriati each won grand slams before the emergence of the Williams sisters.
But in March 2009, things had got so bad for American women that only three - Serena Williams, Venus Williams and Bethanie Mattek-Sands - were ranked inside the top 100.
The outstanding performances of the Williams sisters had masked a void for a number of years but the emergence of a number of players from the juniors appears to be changing things.
Eight of the 11 are under 25 and three including Sloane Stephens, tipped to eventually become the world number one by Serena Williams, have yet to turn 20.
"It's tough following the Williams sisters," said Jamie Hampton, who reached round two on Tuesday with a 6-2 6-4 win over 31st seed Urszula Radwanska of Poland.
"We all played juniors and when one of us does well, the others look at it and think if she did it, I can do it.
"I think we all have our own unique personalities and our own unique games. And all our games are very good and they're all going to mature at different times."
(Editing by Mark Meadows; firstname.lastname@example.org; +44 20 7542 7933; Reuters Messaging:; email@example.com)