The much-hyped temporary exit of William Petersen’s character from “CSI” last night boosted the veteran crime drama to its best numbers of the season. Of course it didn’t hurt that fellow 9 p.m. timeslot occupant “Grey’s Anatomy” was a repeat last night on ABC.

“CSI” averaged an 8.3 adults 18-49 rating and 25.9 million total viewers, according to Nielsen overnights. That was the first time this season the show has jumped above an 8.0.

In fact, just a few weeks ago it neared series lows in competition with original episodes of “Grey’s.”

But CBS heavily promoted Petersen’s four-week exit to return to his stage roots. During its Sunday NFL games the past few weeks, there were loads of ads teasing Gil Grissom’s departure. He’ll return after Liev Schreiber finishes a guest stint.

“CSI’s” ratings have fallen 16 percent from last season, in part due to the tough competition from “Grey’s.” When “Grey’s” is in repeats, the show performs noticeably better. In its final episode of 2006, airing opposite a “Grey’s” repeat on Dec. 7, “CSI” averaged a 7.8, its second-best rating of the season.

“CSI” helped CBS to a comfortable first-place finish for the night among 18-49s, as the network averaged a 5.2 rating and a 13 share. NBC finished second at 4.1/10, ABC third at 3.8/10, Fox fourth at 1.9/5, Univision fifth at 1.8/4 and CW sixth at 1.1/3.
 
Though CBS finished first for the night, NBC took the first hour with a 4.3 average rating at 8 p.m. for “My Name is Earl” (a season-high 4.3) and “The Office” (4.3). ABC was second that hour with a 3.7 for “Ugly Betty,” CBS third with a 3.5 for a “CSI” repeat and Univision fourth with a 2.3 for “La Fea Mas Bella.” That left Fox fifth with a 2.0 average for “‘Til Death” (2.0) and “The War at Home” (2.0), and CW sixth with a 1.0 for a repeat of “Smallville.”
 
At 9 p.m. CBS led the hour with an 8.3 rating for “CSI.” ABC remained second with a 3.7 for a “Grey’s Anatomy” rerun, with NBC falling to third with a 3.3 average for “Scrubs” (3.6) and “30 Rock” (3.0) and Fox jumping to fourth with a 1.7 for the recently canceled “The O.C.” Univision dropped to fifth that hour with a 1.6 for “Mundo de Fieras” and CW stayed in sixth place with a 1.1 for another “Smallville” repeat.
 
NBC jumped back into the lead at 10 p.m. with a 4.6 for “ER.” ABC was second with a 4.0 for another repeat of “Grey’s,” CBS third with a 3.7 for “Shark” and Univision fourth with a 1.4 for “Aqui y Ahora.”
 
Among households, CBS was first for the night with an 11.2 average rating and a 17 share. ABC was second at 7.1/11, NBC third at 5.8/9, Fox fourth at 2.9/4, Univision fifth at 2.3/3 and CW sixth at 1.7/3.