Aug. 28-Sept. 10 US Open tennis championships Those who'd like to greatly limit their TV viewing of the Open, which began Monday, should consider tuning in Sept. 9. That's Super Saturday, when the men's semifinals are sandwiched around the women's final. The tournament's $64,000 question: Can anybody stop Monica Seles, who is bigger and possibly better than ever? She prevailed in '91 and '92 but was forced to miss the last two Opens, won by Steffi Graf and Arantxa Sanchez Vicario. Sept. 3 National Football League season opens After a spectacular 75th anniversary season, the NFL goes to work on an encore. The San Francisco 49ers plan to be at the heart of it, as they seek to repeat as Super Bowl champs behind quarterback Steve Young. Oddly, Los Angeles will be without a team for the first time since 1945, as both the Rams and Raiders have shipped out - the Rams for St. Louis and the Raiders back to Oakland. Elsewhere in California, the San Diego Chargers will try to prove that last season's journey to the Super Bowl was no fluke. On the opposite coast, two new franchises begin play in Jacksonville, Fla. (Jaguars) and Charlotte, N.C. (Carolina Panthers). Sept. 4 US Nationals (drag racing) This is the oldest, most prestigious, and richest drag race in the National Hot Rod Association's year-long series. Indianapolis Raceway Parks hosts this year's 41st annual championships. Sept. 19-24 Rhythmic gymnastics world championships Working with various apparatus - rope, ball, clubs, and ribbon - women gymnasts will perform floor exercises to either taped or live music. No doubt some competitors will pick waltzes for their routines, since the competition is in Vienna. Rhythmic gymnastics made its Olympic debut in 1984. Sept. 22-24 Davis Cup tennis semifinals What began with 16 national teams in January is down to the final four. Which players will compete from one round to the next is often uncertain, yet the big names in men's tennis are always more likely to show when it reaches this point. Defending champion Sweden travels to Las Vegas to take on the US team and most likely hometown hero Andre Agassi. In the other semi, Russia hosts Germany in Moscow. Sept. 22-24 Ryder Cup (golf) This is the team event that actually seems to excite players: US vs. Europe. It is named for Samuel Ryder, a wealthy British seed merchant who put up a gold trophy for the inaugural 1927 matches between British and American golfers. The format was broadened to include other European nations in 1979. Twelve-man squads will square off at the Oak Hill Country Club in Rochester, N.Y. Sept. 23-24 Mountain biking world championships The Black Forest in Kirchzarten, Germany, provides a scenic venue easily reached by Swiss, Italian, and French cycling fans. One of the anticipated attractions among the cross-country and downhill events is the men's cross-country final, a seven-lap race that should take more than two hours to complete. Half a world away, in Bogota, Colombia, track cycling's world championships will be held on a steeply banked, cement velodrome Sept. 26-30. Top speeds will reach 40-45 m.p.h.