With CBS’s “Survivor” already done for the season, ABC lengthened its lead on the final Thursday of sweeps, finishing well ahead of second-place NBC for its fourth straight May sweeps Thursday victory.

Last night ABC averaged a 4.5 adults 18-49 rating and 12 share, according to Nielsen overnights, 29 percent ahead of second-place NBC’s 3.5/9. CBS, which aired a repeat of “CSI” in place of “Survivor” at 8 p.m., finished third for the night at 3.4/9, a week after challenging ABC for the nightly lead.

“Grey’s Anatomy” slipped 8 percent from the previous week, from a 6.4 to a season-low 5.9, but it was still the night’s top-rated show among adults 18-49. Its 9 p.m. competitor, “CSI,” had its lowest-rated season finale ever, averaging a 4.7.

“CSI” did best “Grey’s” among total viewers, with 17.7 million to the latter’s 15.2 million. “Grey’s” airs its two-hour season finale next week.

ABC’s “Lost” did improve week to week, averaging a 5.0 in 18-49s at 10 p.m., up 6 percent from last Thursday. It won its timeslot for the fourth straight week and was the night’s No. 2 show in the demo. “Lost’s” season ender airs in two weeks.

Meanwhile, on a night full of season finales, Fox finished fourth for the night at 2.3/6, Univision fifth at 1.7/5 and CW sixth at 1.4/4.
 
NBC started the night in the lead with a 3.0 rating at 8 p.m. for “My Name is Earl,” followed by ABC with a 2.7 for “Ugly Betty.” Fox was third with a 2.2 for “Are You Smarter than a 5th Grader?,” Univision fourth with a 2.1 for “Al Diablo con los Guapos” and CBS and CW tied for fifth at 1.7, CBS for a repeat of “CSI” and CW for “Smallville.”
 
ABC took the lead at 9 p.m. with a 5.9 for “Grey’s,” while CBS jumped to second with a 4.7 for “CSI.” NBC was third with a 4.1 for “The Office,” Fox fourth with a 2.3 for “Don’t Forget the Lyrics,” Univision fifth with a 1.9 for “Fuego en la Sangre” and CW sixth with a 1.2 for “Supernatural.”
 
At 10 p.m. ABC led again with a 5.0 for “Lost,” with CBS second with a 3.6 for “Without a Trace.” NBC was third with a 3.3 for “ER,” its best rating since January, and Univision fourth with a 1.2 for “Amas de Casa Desperadas.”
 
CBS was first for the night among households with an 8.7 average overnight rating and a 14 share. ABC was second at 7.8/13, NBC third at 5.1/8, Fox fourth at 4.7/8, CW fifth at 2.1/3 and Univision sixth at 2.0/3.