Round one continues on day two of the 2012 US Open, as four former US Open champions lead a formidable field into action at the USTA Billie Jean King National Tennis Center. Defending men’s champ Novak Djokovic, Serena Williams, VenusWilliams and Andy Roddick all play first-round matches today, headlining a host of the game’s top talents in pursuit of tennis’ toughest title.

No one has had a more sizzling summer than Serena Williams, who captured her 14^th career Grand Slam singles title at Wimbledon, then followed that up with a win at Stanford and a pair of gold medals (winning singles and doubles) at the London Olympics. The three-time US Open champion has won five tournament titles this year, compiling a 46-4 record coming into this event. Williams may be seeded No. 4, but don’t let that fool you—she’s clearly the number one pick to finish first here. She’s played all summer with the sort of focus that suggests her sights are set squarely on a second-Saturday showing. Williams will be very familiar with her first-round opponent this evening, 20-year-old American Coco Vandeweghe, having beaten her last month in the Stanford final—one of two finals Vandeweghe has reached this year. Vandeweghe is certainly a talented up-and-comer, but Williams may well be playing her best tennis right now and owns a 47-1 record in first-round matches at Grand Slam tournaments. That’s a lot to overcome. In two, Williams advances.

This is only the third time in the 14 years she’s competed here that Venus Williams is unseeded at the US Open. Twice a champion here—and four times a finalist—Williams has been hampered in recent years by an auto-immune disease that has limited her play. Still, the former No. 1 comes to Flushing Meadows on the heels of a gold-medal doubles run at the Olympics and a solid semifinal showing in Cincinnati, where she scored an impressive win over Samantha Stosur in the quarters. Even without a number next to her name, Williams still figures as a factor in Flushing. Today, she takes on fellow American Bethanie Mattek-Sands, who has struggled to find her feet after injuring her shoulder in 2011. In seven events this year, Mattek-Sands has yet to advance beyond the second round, and she comes in having lost back-to-back first-round matches at Cincinnati and New Haven. Williams has won all three of their career meetings, though the two have not gone head-to-head since clashing here in 2009. Neither player is at her best, but Williams is still the better player. She’s through in straights.

Women’s No. 2 seed Agnieszka Radwanska has enjoyed a breakthrough year in 2012, winning three tournament titles and reaching her first career Grand Slam tournament final at Wimbledon—the first Polish player in the Open era to reach a major final. But the 23-year-old has never been beyond the fourth round here—advancing that far in both 2007 and 2008—and she was forced to retire in the second round at New Haven last week with a shoulder injury. It will be interesting to see how that injury will factor into this faceoff with Nina Bratchikova, a 27-year-old Russian who this year has reached the third round at both the Aussie and French Opens. Bratchikova took a set off Petra Kvitova at Roland Garros, and she’s certainly capable of doing the same here to Radwanska, especially if the second seed is not 100 percent. In a close three, Radwanska moves on.

After a spectacular 2011 season in which Djokovic compiled a staggering 70-6 record, won his first US Open title and ascended to No. 1 in the world, the 25-year-old Serbian superstar has come back into our stratosphere—at least slightly—in 2012. That said, it’s still a stratosphere in which he captured his fifth career major title at the Australian Open, reached his seventh Grand Slam tournament final at the French, and compiled a 54-10 match record that is second only to Roger Federer’s among the men. What’s more, Djokovic’s play this summer earned him the Emirates Airline US Open Series men’s title—meaning he’s playing here for a potential $1 million bonus. That’s not a bad stratosphere in which to live. Djokovic opens up the defense of his US Open crown tonight against Italy’s Paolo Lorenzi, who’s playing in his first US Open main draw. The Serb has won their two previous encounters, including a straight-set thrashing of the Italian in the first round of this year’s Aussie Open. In that match, Lorenzi won two games—and it doesn’t figure to get any easier for him tonight. In three, Djokovic is on to round two.

One of the day’s more intriguing matchups pits 2003 US Open champ—and perennial Flushing fan favorite—Roddick against a fellow American, qualifier Rhyne Williams. Williams, the 2011 NCAA runner-up while at the University of Tennessee, played his way through qualifying and into his first Grand Slam tournament main draw without losing a set, demonstrating a gritty game and unwavering resolve. At 21, Williams is the same age Roddick was when he won his only career Slam singles title here, and the qualifier looms as a solid test for the former No. 1, who’s had an up-and-down season so far. Roddick, who will turn 30 on Thursday, has taken two titles this year, but his third-round showing at Wimbledon is his best performance at a Slam in 2012. Roddick played well in winning the Atlanta hard-court event in July, but suffered a bad loss to No. 74-ranked Steve Darcis at Winston-Salem last week. The big stage of Ashe would seem to favor the experienced Roddick, but Williams doesn’t seem the type to be overwhelmed by either opponent or occasion. This could be a good one. Give Williams a set, but Roddick advances in four.

• Andy Roddick Bio