Maybe smartweed? Polygonum spp.
hortster

Perhaps Commelina?

Japanese stiltgrass? That is what I have everywhere! I used a pre-emergent crabgrass preventer with the chemical Dimension in spring and got good control. This is an annual grass that seeds prolifically.

I say stiltgrass too, from sad familiarity with the little buggers. I have it in my gardens, not my lawn, so herbicide use is out for me. Here's a page from one of the invasive plant websites, with some recommendations for control. Good luck!

Here is a link that might be useful: Stiltgrass