Tennis usually comes to a standstill at this time of year for the game’s best players, and most of all for American fans, who have to look to China, Japan, India, and Europe for a post-U.S. Open fix. Most of the tennis they find doesn’t include stars like Roger Federer, Andy Roddick, Maria Sharapova, or Rafael Nadal.

It also almost never involves Venus or Serena Williams, who are more likely to tend to their injuries — or their many fashionable business ventures — during fall. But this season brings a welcome change. In what must be seen as a hopeful sign by American fans — so hungry for young talent, and so nervous that coming years will bring a veritable famine — the sisters are playing tennis. Lots of it. Two weekends ago, Venus won a tournament in Seoul, South Korea, while dropping just one set. In Japan this weekend, she lost a shocker to Virginie Razzano, 4–6, 7–6(9–7), 6–4 in the final, despite holding three match points in the second set. Venus struggled with a minor hamstring injury, but she still plans to play again this week in Bangkok, Thailand, where she will complete her Asian swing before either returning to Europe for a larger tournament in Zurich, Switzerland, or heading straight for the season-ending championships in Madrid in November. She’s won three titles this year — including Wimbledon — her most since 2002, when she won seven, and is now ranked no. 8 in the world.

Serena shook off her U.S. Open defeat to Justine Henin by playing the Porsche Tennis Grand Prix in Stuttgart, where she lost to Svetlana Kuznetsova (Henin went on to win the title and continues to play the best tennis of her career). This was the first time Serena has played a tournament after the U.S. Open since 2004, when she lost in the first round in Beijing in her last event of that year. Serena has three more events on her calendar — Moscow (this week), Zurich, and the season-ending event in Madrid — and is ranked no. 7 in the world.

The practical view of this late-season tennis spree by the Williams sisters centers on ranking points (and perhaps some appearance fees that might explain Venus’s preference for small tournaments over those with more prize money). Both sisters are close to qualifying for Madrid, and they can guarantee themselves an appearance with a few more victories. In this case, a few ranking points can mean a lot of money: The championship offers the biggest prize other than the Grand Slams, and neither of the sisters has taken a cut of that cash since 2004, when Serena lost in the final to Maria Sharapova.

Yet the Williams sisters have treated their rankings with so little regard the last few years that it seems odd to think they are suddenly concerned about them now. What’s more likely, and more encouraging, is that they are tiring of playing only a handful of tennis matches a year and rolling the dice at major tournaments. As we’ve seen this year, the sisters can win any event (as they did in Australia and at Wimbledon) no matter their form heading into it. But they can lose, too, especially with Henin playing as well as she is (Henin knocked Serena out of the French Open, and at the U.S. Open defeated both sisters back-to-back in what ranks among the greatest performances in the history of the game).

Since returning from a wrist injury in the early part of the season, Venus has been one of the most committed players on the tour. So far this year, she’s played 56 matches, the same number she played in all of 2004, and tied for the third most matches she has played in a single season in her career. Her no. 8 ranking is up 40 places from the end of last year.

Serena hasn’t quite fulfilled the hopes many had for her after she won the Australian Open and talked about regaining the no. 1 spot in the world. But she has seemed more motivated in recent months — perhaps because of the way Henin has beaten her in three consecutive Grand Slam events. No surprise that Henin won at the French Open, and Serena wasn’t fully healthy at Wimbledon, after taking a bad fall in her previous match. At the U.S. Open, however, Henin scored her most decisive victory, and there could be no excuses from Serena — at least no viable ones, and certainly not the “lucky shots” she cited in her five-minute display of poor sportsmanship that passed for a post-match press conference.

To beat Henin — at least a healthy Henin — Serena has to work harder, and she knows it. She’s still not in top shape. She still gets by with lazy footwork from time to time, especially late in matches. She still depends too much on her serve and not enough on the approach shots that used to bring her to the net for winning volleys, usually of the swinging variety. It wouldn’t hurt if she would play Henin later than the quarterfinals at major events. The only way to ensure that is to play more and improve her ranking.

By the time the Tour Championships roll around next month, either one of the sisters could be ready to defeat Henin and give the rest of the field something to think about for next year. It’s high time they did: The last time both sisters played in the season-ending championships was 2002. Serena has won the title once, in 2001, back before it featured the round-robin format first adopted by the men’s tour. Venus has only played it twice and lost in the semifinals both times.

American tennis fans haven’t had much to look forward to the last few years, but if this season is a sign of things to come from the Williams sisters, that bleak outlook could change. Venus celebrated her 27th birthday in June; Serena turned 26 in September. For athletes of their caliber, playing well until age 32 or 33, even 34 or 35, wouldn’t be a stretch, especially when the two best groups of players behind them — one mostly Russian, the other from Serbia and several Eastern European countries — do not have the talent of the Williams sisters. With any luck, Serena and Venus will make us forget about the future for years to come.

Mr. Perrotta is a senior editor at Tennis magazine. He can be reached a tperrotta@nysun.com.