ABC 7's Mark Giangreco, Cheryl Burton, Ron Magers, Kathy Brock and Jerry Taft

In a last-ditch effort to stave off defeat in the May sweeps, perennial market leader WLS-Channel 7 is pulling out all the stops — and some of the commercials — from its 10 p.m. Monday through Friday newscast.

On Monday and Tuesday night, the ABC-owned station dropped two commercial breaks from its late news, postponing its first interruption until 10:21 p.m. It’s a maneuver designed to retain audience ratings by discouraging viewers from channel surfing.

WMAQ-Channel 5, which has used the ploy in the past, responded by dropping its commercial breaks until 10:22 p.m. Tuesday. The NBC-owned station is poised to overtake ABC 7 among viewers between 25 and 54 — a key demographic driving advertising revenue.

The move does not appear to have benefitted ABC 7 after all. As of Wednesday, NBC 5 continues to lead at 10 p.m. with a 3.6 percent share of the 25-to-54 audience over ABC 7’s 3.4 share. Both stations are up compared with last May, but NBC 5 gained more ground.

As measured by Nielsen Co., the May sweeps began April 23 and end Wednesday night.