NBC 5 may have top story at 10 p.m.

Rob Stafford and Allison Rosati

Rob Stafford and Allison Rosati

With three days to go in the May sweeps, all eyes are on Chicago’s late-news ratings race, where there could be an upset in the works.

NBC-owned WMAQ-Channel 5 appears poised to overtake the market’s perennial front-runner, ABC-owned WLS-Channel 7, among viewers between 25 and 54 at 10 p.m. Monday through Friday. That’s a key demographic driving local stations’ advertising revenue.

As of last Friday, NBC 5’s 10 p.m. newscast, anchored by Allison Rosati and Rob Stafford, was averaging a 3.6 percent share of the 25-to-54 audience — up from 3.1 in April and 2.9 last May. ABC 7’s 10 p.m. newscast, anchored by Kathy Brock and Ron Magers, had a 3.4 share in the demo — up from 3.3 in April and 3.2 last May.

Running a distant third is the 10 p.m. newscast on CBS-owned WBBM-Channel 2, anchored by Kate Sullivan and Rob Johnson, with a 0.9 share — flat from April and down from 1.1 last May. Despite viewer interest in the final weeks of David Letterman’s “Late Show,” CBS 2 is believed to be among the worst performers among the network’s major market stations.

Among 9 p.m. newscasts, Fox-owned WFLD-Channel 32 continues its free fall with news anchors Dawn Hasbrouck and Jeff Herndon averaging a 0.9 share — down from 1.1 in April and 1.3 last May. Tribune Media WGN-Channel 9, anchored by Micah Materre and Mark Suppelsa, remains steady with a 1.6 share — flat from April and up from 1.5 last May.

As measured by Nielsen Co., the May sweeps began April 23 and run through Wednesday.