After stumbling in the dark all summer, CW turned the lights on Monday with promising preems for returning dramas “Gossip Girl” and “One Tree Hill.”

The drama duo, paired on the night for the first time late last season after the net’s comedy block disappointed, combined to give CW its best Monday to date in key demos.

Numbers must be a sigh of relief for execs at the netlet, which is heading into a potentially pivotal third season and looking to strengthen its sked one night at a time. The CW, which had barely registered in the Nielsens over the summer, was taking a bit of a risk by launching on Labor Day.

Its biggest chip of the fall, of course, is the new rendition of “90210,” which bowed Tuesday night.

According to preliminary Nielsen nationals, the second-season premiere of “Gossip Girl” (1.7 rating/6 share in adults 18-49, 3.4 million viewers overall) hit series highs in 18-49 as well as the net’s target demo of adults 18-34 (2.3/7). It ran second to Fox’s “Prison Break” in adults 18-34 and led its hour in women 18-34 (3.2/10).

Show bowed against tougher competish a year ago yet benefited from airing behind the net’s top-rated show, “America’s Next Top Model.”

Since then, however, “Gossip” has developed enough of a core following to lead off a night and is helping bring good flow to its similarly sudsy lead-out “One Tree Hill.” That WB Network alum keeps chugging along despite receiving a fraction of the media buzz of its ballyhooed skedmate.

The sixth-season preem of “One Tree Hill” (prelim 1.6/4 in 18-49, 3.1 million viewers overall) retained 100% of its “Gossip Girl” lead-in among adults 18-34, winning its hour in women 18-34 (3.3/9). In various categories, it either matched or bested its season highs of last season.

Combined, the dramas gave CW its best Monday ever in adults 18-34 (2.3/7) and some key female demos. It was the night’s top-ranked network among adults 18-34 in top-10 markets New York, Chicago, Washington and Houston.

Monday also saw Fox’s “Prison Break” launch its fourth-season with OK numbers for a two-hour premiere (prelim 2.6/7 in 18-49, 6.5 million viewers overall). It peaked with a slot-leading 2.8/7 in the demo and 6.8 million viewers overall from 9 to 10 p.m., where it will regularly air this fall.

Though on the low end of the show’s ratings range — last season’s preem averaged a 3.3/9 in 18-49 — it’s not a bad bow for Labor Day. Also, unlike last year, when it preemed a couple of weeks later, it didn’t benefit from heavy NFL promotion the previous day.

NBC placed second to Fox on the night in 18-49 and won in total viewers with its nonscripted combo of “Deal or No Deal” (prelim 2.8/8 in 18-49, 10.9 million viewers overall) and “America’s Toughest Jobs” (2.6/7, 7.5 million). “Chuck” and “Heroes” move in to kick off their seasons on the night later this month.