Fast National ratings for Thursday, April 15, 2010.
 
"CSI" was Thursday's most watched show, while "Survivor: Heroes vs. Villains" was the night's best in the key demo, so it's no wonder that CBS claimed the evening's key ratings races.
 
Meanwhile, NBC got solid demo numbers from a "Saturday Night Live" documentary special and "FlashForward" went back to losing viewers.
 
Among adults 18-49, CBS averaged a 3.1 rating for the night, topping the 2.6 rating for FOX and ABC's 2.4 rating in the all-important age range. ABC and The CW tied for fourth with a 1.3 rating.
 
Overall, CBS averaged an estimated 12.23 million viewers to go with a 7.5 rating/13 share. FOX's 5.1/9 was second, topping the 3.7/7 for NBC. ABC's 3.1/5 was fourth, comfortably holding off the 1.6/3 for The CW in fifth.
 
"Survivor: Heroes vs. Villains" kicked Thursday off in first for CBS with a 7.1/12, also delivering a 3.7 demo rating. FOX's "Bones" was a strong second with a 6.2/11, also improving slightly from last week in the demo. ABC's "FlashForward," inexplicably up last week, fell to a 3.4/6 dropping under 5 million viewers and a to a 1.4 demo rating. NBC's two episodes of "The Office" were fourth. The CW's "The Vampire Diaries" had a 1.8/3 and although it last half-a-million viewers from last week, "VD" did a 1.5 demo rating to beat "FlashForward."
 
In the 9 p.m. hour, "CSI: Crime Scene Investigation" had an 8.1/14 for CBS, drawing 13.05 million viewers and winning the hour with a 3.0 rating in the demo. NBC's tribute to last decade on "Saturday Night Live" was second with a 4.2/7 and in the demo. FOX's "Fringe" had a 4.1/7 and actually beat NBC in total viewers, showing a little improvement from last week. ABC's "Grey's Anatomy" repeat was fourth. The CW's "Supernatural" had a 1.5/2 for the hour.
 
A repeat of "The Mentalist" had a 7.5/13 to win the 10 p.m. hour for CBS. NBC's "SNL" special was second overall with a 4.2/8 and won the hour in the demo with a 3.0 rating. ABC's repeat of "Private Practice" was third.
 
 
All ratings information comes from preliminary Fast National Nielsen data, which includes live and same-day DVR viewing. All numbers are subject to change.