LOL!! That's woolly yarrow and try spot applications of any broadleaf lawn herbicide.

FWIW, it is virtually impossible to have a pristine, weed-free lawn without using copius amounts of chemicals. I believe developing an acceptable level of tolerance is easiest on the homeowner as well as far less disruptive to the environment. Woolly yarrow is actually sold as a lawn substitute - not a bad choice, all in all. Low growing, soft on bare feet and will retain its foliage and color in our dry summers without the need for the constant, wasteful irrigation turf lawns require.

Lawns are more interesting with flowers in them.

I'd hate to walk barefoot in a weed-free lawn, what with all those chemicals.....

Or course with flowers you may have to watch for bees. Everything has a flip side.