NEW YORK — 98 Degrees and Jessica Simpson sang and strutted through four smooth hits for a sellout family crowd of 28,038 at the National Tennis Center in Queens for the U.S. Open's all-day Arthur Ashe Kids Day festival Saturday.

The pop performances were part of the kickoff of the U.S. Open tennis tournament, which begins Monday (Aug. 28) and ends Sept. 10.

Simpson and 98 Degrees each performed slick sets backed by multipiece bands and dancers, all crammed efficiently onto a small stage on an upper tier of Arthur Ashe Stadium. Their familiar-sounding beats sounded blurry as they boomed from the arena's speakers.

98 Degrees — brothers Nick and Drew Lachey, Jeff Timmons and Justin Jeffre — were the first and last to perform. Both times, they were casually dressed in dark and baggy clothes. Female dancers, wearing tight tops and gauzy, colorful skirts, ran their hands up and down the singers' bodies.

The foursome began by crooning "The Hardest Thing," from their most recent album, 98° and Rising (1998). (The band's next record, Revelation, comes out Sept. 26.)

Girls screamed and waved signs proclaiming their loyalty to the bandmembers, who traded solos on their swooning R&B-flavored ballads.

"I like the beats and the dancing," Robin Chu, 17, of Queens, N.Y., said. "My friends think they're good-looking, although I don't really."

With a whoosh, Simpson's band kicked into a pleasing synth wash that boomed throughout the stadium, leading into "I Think I'm in Love With You," the second cut from her debut album, Sweet Kisses (1999).

The 19-year-old singer was backed by her five-piece band, eight dancers in matching white-and-blue outfits and two backup singers. Later, Simpson and Nick Lachey sang their signature duet, "Where You Are," from Simpson's album.

They clasped hands during much of the song, letting go only to symmetrically and passionately gesticulate at the sky during the duet's most emotion-soaked passages.

The final music bit belonged to 98 Degrees and their current, Latin-tinged single, "Give Me Just One Night (Una Noche)."

"Everyone was insanely gorgeous," Yannick Riveti, 17, of Manhattan, said of the pop stars and the dancers, on the way out of the stadium. "The crowd was so into it."

Co-hosted by CBS announcer Mark McEwen and VH1 VJ Roshumba Williams, and broadcast nationally on CBS on Sunday, the show featured tennis exhibitions as well as appearances by celebrities, including actress Jennifer Love Hewitt and current #1 ranked tennis stars Andre Agassi and Martina Hingis. (Sonicnet.com's parent company, Viacom, also owns VH1 and CBS.)

The fifth annual Kids Day benefited the National Junior Tennis League, a program to teach tennis to economically disadvantaged kids that was co-founded in 1969 by late tennis great and black sports pioneer Arthur Ashe.