“Survivor: Marquesas” emerged a winning warrior on Sunday, fending off tough and varied competition and helping CBS to easily win the night.

Sterling Sunday has locked up CBS’ second-place finish for the sweep in adults 18-49 — its highest May standing since demos were first tracked in 1987. Net’s projected average (4.1) would be its highest in five years.

NBC’s “The Cosby Show” reunion show and Fox’s “The X-Files” series finale also performed well Sunday. ABC’s two-hour “The Practice” season finale took its lumps opposite the competish, but even it rallied to some solid numbers by the final hour.

According to Nielsen prelims, from 9-10 p.m., the four major networks combined for a 59 share in adults 18-49 — way up from both last week’s 45 share and the 47 share the nets drew on the final Sunday of the May 2001 sweep.

Leading the way was “Survivor,” whose fourth edition wrapped with a projected average of 26 million viewers and a 10.5 rating/24 share in adults 18-49 from 8-10:10 p.m.

When numbers are finalized by Nielsen today, the two-hour “Marquesas” finale should come in down about 5% from the “Africa” finale in January. The two editions also should finish with similar overall averages, signaling something of a leveling off for the franchise, whose opening two editions posted huge ratings.

Combined with “60 Minutes” and a roughly 55-minute “Survivor Reunion” show hosted by Rosie O’Donnell, CBS won Sunday across the board, with preliminary Nielsen averages of 8.0/19 in adults 18-49, 8.9/20 in adults 25-54, 7.3/19 in adults 18-34 and 21.4 million viewers overall.

Excluding the Super Bowl and Olympics, the 8-10 p.m. segment of “Survivor” produced the Eye net’s best adults 18-49 and 25-54 showings in the time period on a Sunday since 1993. And in adults 18-34, the 9.6/24 is the best Sunday entertainment score on record for CBS.

The “Survivor Reunion” show won its time period in adults 18-49 (prelim 8.3/19) and 25-54 (prelim 9.0/19), while finishing second to the “Cosby Reunion” in viewers (prelim 18.3m).

NBC, boosted by “Cosby” from 9 to 11, ran second on the night in 18-49 (prelim 5.8/14), 25-54 (6.0/13) and total viewers (roughly 13.6 million).

Reunion show, which featured series stars and included clips from the immensely popular 1980s laffer, averaged roughly 18.2 million viewers and a 7.6/17 in adults 18-49. This makes it easily the best performer of the nostalgic month’s six series reunion specs.

At Fox, “X-Files” wrapped its nine-season run with a two-hour episode (8-10 p.m.) that produced the series’ top scores since last season’s finale (prelim 13m, 6.1/14 in A18-49). Episode, which featured David Duchovny and promised to answer many of the program’s mysteries, came within about 3 shares of “Survivor” in “X’s” strongest category, men 18-34 (7.1/17 vs. 8.5/20).

Fox’s “The Simpsons” won the 7:30 half-hour in 18-49 (prelim 5.2/16).

ABC’s “The Practice” was snowed under at 9 (prelim 11.3m, 3.5/7 in A18-49), but picked it up with its second episode at 10, which delivered the show’s best numbers since January (prelim 15.1m, 5.2/12).

By easily defeating ABC on the night, Fox appears to have locked up third place for the sweep in adults 18-49. After the nets ran neck-and-neck for much of the month, Fox’s finales and specs are proving the difference down the stretch.