Justin Timberlake has maintained his lead at the top of the US pop charts for a third week. The pop star's SEXYBACK hit holds firm at number one on the Billboard Hot 100 chart, fending off a charge from Fergie's LONDON BRIDGE - the song he knocked off the top. The Pussycat Dolls' BUTTONS hit, which features Snoop Dogg, is also challenging for the number one spot after climbing from four to three. Meanwhile, Ok Go's treadmill-dancing performance at the MTV Video Music Awards at the end of last month (AUG06) seems to have paid off - their HERE IT GOES AGAIN tune is this week's greatest sales gainer, jumping from 87 to number 38 on the new chart. Beyonce Knowles scores the chart's top debut with RING THE ALARM, which enters at number 12 and is also the singer's highest ever debut. In other US pop charts, Janet Jackson scores her 15th number one on the R+B/Hip-Hop Songs chart with her duet with Nelly, CALL ON ME, climbing six places.