With 27 million viewers, last Tuesday's performance edition of American Idol ranked as the most-watched show of the week and helped Fox edge out NBC among adults 18-49. CBS came out on top among total viewers, thanks to its strong Monday lineup and a decent performance from its NCAA basketball tourney. Meanwhile, first-year shows Las Vegas, The O.C., The Apprentice and Extreme Makeover: Home Edition posted their best ratings of the season last week.