Fox's critically praised new drama "Prison Break" didn't equal last week's strong premiere, but all things considered it held up pretty well.
   The show averaged a 3.9 adults 18-49 rating last night, according to Nielsen overnights, down 15 percent from last week's 4.6 for its two-hour debut.
   Some dropoff was to be expected, however, over the holiday weekend. Many people travel on Labor Day, and some may not have expected a new episode on a traditionally quiet day for television.
   Also, ABC aired an exciting college football game between Miami and Florida State opposite "Prison" last night, much stronger competition than the show saw last week.
   Best of all for Fox, “Prison” is improving on the most recent numbers for its 9 p.m. timeslot. The show’s two-week 4.3 average is up 5 percent over Fox’s 4.1 Monday night average during the 2004-’05 season and up 65 percent over the network’s summer average of 2.6.
   “Prison” averaged 8.47 million total viewers last night, a 19.0 percent drop 10.46 million last week.
   “Prison” was the most-watched show among viewers 18-49 last night, though ABC finished first in the demo with a 3.5 average rating and a 9 share. CBS was second at 3.2/8, Fox third at 3.1/8, NBC fourth at 2.0/5, and the WB and UPN tied for fifth at 0.8/2.
   At 8 p.m. ABC led with a 3.4 average for the first hour of the FSU-Miami game. NBC was second with a 2.6 for “Dateline,” while CBS averaged a 2.3 rating for repeats of “The King of Queens” (2.2) and “Everybody Loves Raymond” (2.5), tying for third with Fox’s “Nanny 911.”
   At 9 p.m. Fox led with its 3.9 average for “Prison Break.” ABC was second with a 3.8 average for the second hour of football and CBS third with a 3.6 for an hour of “Two and a Half Men.”
   CBS took the lead at 10 p.m. with a 3.7 average for a repeat of “CSI: Miami.” ABC was second with a 3.2 for the last hour of college football and NBC third with a 1.8 for a repeat of “Medium.”
   ABC and CBS tied for first for the night among households, each with a 6.3 average rating and a 10 share. NBC and Fox tied for third at 4.3/7, with the WB fifth at 1.6/2 and UPN sixth at 1.2/2.