After taking a first-round bye, top seed and defending two-time 50s champion Ros Nideffer will play her opening round singles match of the USTA National Women’s 50-90 Hard Court Championships today, May 10, at the La Jolla Beach & Tennis Club. Nideffer, who is attempting to win her third straight 50s singles title and fourth overall, will face San Diego’s Nancy Abler-Sanchez at 11:30 a.m. Abler-Sanchez, unseeded, defeated Jill Sickle of Chicago 6-3, 7-6 (2) in May 9 first-round action. The 55-year-old Nideffer, of Rancho Bernardo, is a former touring tennis professional. In 1990, she reached a career-high No. 15 in the Women’s Tennis Association singles rankings. She is also a two-time Wimbledon singles quarterfinalist and a former French Open doubles champion. In other first-round action on May 9, Brenda Carter, of Charleston, S.C., top seed in the 70s singles division, cruised into the second round with an impressive 6-0, 6-0 victory over Emina Minka Kulenovic of La Jolla. Carter, who turns 70 next month, has been playing tennis for more than 50 years and has earned 48 gold USTA balls for national championships in various singles and doubles divisions. After receiving first-round byes, the top seeds in the 60s singles division will play their second-round matches May 10.  Top-seed and defending champion Tina Karwasky, of Glendale, faces San Diego’s Sue Sprague, and second-seeded Carolyn Nichols, of Rancho Santa Fe, will play Ginny Beneke, of San Diego. Both matches are scheduled to begin at 10:30 a.m. Start times for each day of the championships are as follows: May 10 through May 13, 8 a.m.; and May 14 and 15, 9 a.m. Friday, May 13 – 8 a.m.; Saturday, May 14 and Sunday, May 15 – 9 a.m. The La Jolla Beach & Tennis Club’s 44th Annual Men’s Senior Championships are also taking place the same week in conjunction with the women’s events and will include both singles and doubles for 60 and over, 65 and over, 70 and over, 75 and over and 80 and over age groups. Although the men’s events are not national championships, they will feature many senior players who regularly compete in national tournaments. More than 300 players are expected for the men’s and women’s tournaments.