Problem Weed in Lawn. Can't figure out what it is

[Jp4wd]

Having a big problem with this weed popping up in fescue lawn. Has anyone seen this before and how can I get rid of it. A lot of shade but some areas do get around 5 hours of sun. It doesn't seem to care. I tilled the lawn last fall and planted with pennington dense shade and it has come in well but this weed seems to be winning in the areas it is in. I live in NJ.

[mrgreenjeans]

I'm in WI and I'm getting the same mystery weed popping up. It does seem to prefer slightly shaded areas. Don't remeber it being there this spring. Probably mid-july when I first started seeing it. Would love to know how to nuke this stuff. It grows so tall it really looks bad!