It's a pair of 30-something Grand Slam champions leading the way, with Roger Federer and Serena Williams not only the most consistent performers on North American hard courts but also wrapping up their US Open preparations by winning the title in Cincinnati over the weekend.
The wins showcase their amazing resiliency yet again, with Federer playing back-to-back Masters finals and Williams getting to the semifinals or further for a third straight week. That means the two have been the top points earners during the US Open series, followed by a mixture of new and familiar figures on both the men's and women's side. (These unofficial rankings look at ranking points earned during US Open Series events, not counting the events being played this week. The US Open Series standings are based on a different points system and give double points for playing more than three events.)
(Tournaments: Masters 1000 Cincinnati, Masters 1000 Toronto, ATP 500 Washington, ATP 250 Atlanta)
The most noticeable names among the men's top 10 US Open Series performers might be the ones not there. No Novak Djokovic, who returned from his Wimbledon victory and subsequent wedding to longtime girlfriend Jelena Ristic with a third-round defeat in Toronto, and also lost at the same stage in Cincinnati.
No Rafael Nadal, who withdrew from the two Masters events with an injured right wrist and Monday dropped out of the US Open. No Australian Open champion Stan Wawrinka or perennial top-10 Tomas Berdych, who did not go deep at either event. No Juan Martin del Potro, who is sidelined following wrist surgery.
But Federer's resurgence means that one of the ATP's Big Four is still on top, while Andy Murray is all the way down at No. 9 with two Masters quarterfinals. At No. 2, however, is Milos Raonic, who is emerging as one of the new names starting to contend for big titles. The 23-year-old Canadian followed up his Wimbledon semifinal with a solid showing on hard courts, winning the ATP 500 event at Washington, reaching the quarterfinals of his hometown event at Toronto and the semifinals of Cincinnati.
Most of the top 10 consists of players who had a big result at one of the two Masters events, which are the biggest of the lead-up tournaments. Jo-Wilfried Tsonga, at No. 3, unexpectedly emerged as the champion in Toronto, turning around an unremarkable season with wins against Djokovic, Murray and Federer. No. 4 David Ferrer was the Cincinnati finalist, while No. 5 Julien Benneteau reached his first Masters semifinal at 32 in Cincinnati, following two good wins in Toronto. No. 7 is a tie between Grigor Dimitrov, another 23-year-old moving up this season, and 32-year-old veteran Feliciano Lopez, who both reached the semifinal in Toronto.
Even though most of the big names competed at only the two Masters, others have benefited from playing more. Vasek Pospisil played all four lead-up events and reached the Washington final, putting him at No. 6. John Isner, the top-ranked American who has played each one of this year's US Open series events, sneaks in at No. 10 despite being up and down, winning the title in Atlanta and reaching match point twice against Murray in the third round of Cincinnati, sandwiched around two opening-round losses at Washington and Toronto. Which will be the better indicator of his US Open showing?
With some of the big names inconsistent or injured during the lead-up events, the rest of the field has been able to take advantage -- something that might also happen at the US Open.
(Tournaments: Premier 5 Cincinnati, Premier 5 Montreal, Premier Stanford, Washington International)
No shortage of recognizable names on the WTA tour recently. Seven of the top 10 US Open Series performers have been ranked No. 1 or won a Grand Slam, with former contenders like Ana Ivanovic and Caroline Wozniacki re-establishing themselves while rising newcomers like Simona Halep and Eugenie Bouchard have blinked.
Way in front is Serena Williams, the champion at the Premier 5 event at Cincinnati and the smaller Premier event at Stanford, who is looking back in charge following first-week exits at the French Open and Wimbledon. Second is Agnieszka Radwanska, who won the other Premier 5 at Montreal and reached the quarterfinals of Cincinnati.
Ana Ivanovic has been climbing back up all season, and the former French Open champion reached the final of Cincinnati by winning a three-set battle against Maria Sharapova to finish third.
One of the biggest developments is the re-emergence of Venus Williams, who has been the fourth-best performer during the US Open Series and is again showing the ability to compete in back-to-back matches and back-to-back weeks. Her long comeback since Sjogren's syndrome was diagnosed in 2011 appears to be reaching a new level. Also playing her best tennis since 2011 is No. 5 Caroline Wozniacki, who has taken Serena to three sets in back-to-back tournaments.
Angelique Kerber, at No. 6, has been solid as usual, while No. 8 Sharapova has been scratchy but, as usual, competing hard. The quiet surprise is No. 7 Ekaterina Makarova, who reached the Montreal semifinals.
Two-time Grand Slam champion Svetlana Kuznetsova is at No. 9 and looks as if she might be ready to have one of her occasional runs, having won the small event at Washington and played good tennis at Cincinnati. Tied for No. 10 are Carla Suarez Navarro, a Spaniard who defeated Sharapova at Montreal, and former No. 1 Jelena Jankovic, who has been winning a few rounds at most events but is still looking to make a big impact.
Some of the big players who have underperformed or not played enough to be among the top 10, like Halep and Petra Kvitova, are also playing this week and might yet locate their form before the US Open. It makes for a crowded field heading into the hard-court major, which should mean a lot of good contests during the two weeks.