From ABC:

The 2-hour return of Alias attracted 7.5 million viewers and a 2.7 rating, 8 share among Adults 18-49. Despite facing Fox's American Idol at 9pm, the Touchstone-produced drama posted its highest Adults 18-49 delivery this season, while drawing its largest audience since its season premiere. Throughout the course of its telecast, Alias grew by 1.3 million viewers and by 35% among Adults 18-49 from its first half-hour to its final half-hour. In its regular 8-9pm time period, Alias improved the time period in both Total Viewers and Adults 18-49 compared to ABC's performance in the hour since Fox's American Idol premiered in January. In its return telecast, Alias was up by 7% in viewers and by 17% in young adults compared to its averages this season.