It looks to me like one of the "Ranunculus" which range from desireable garden plants to invasive "weeds". These have simply moved into your lawn, not killed it, because they have found a good environment to grow in.
To eliminate them might mean using some "weed" killer, with care since you do need to eliminate the roots to kep them from regenerating as they have.

Creeping buttercup, ranunculus repens - nothing desirable about it :) You're going to have to stay diligent to get rid of it, stay rid of it.

Common in W Washington and W Oregon, if you find it returning after you've dug it out, you may have missed some roots - and the seeds are viable for many years. Possibly try spot treating the 'resprouts' with some like Scotts Ecosense Weed Be Gone for lawn weeds, it may help you gain control.

Here is a link that might be useful: Creeping Buttercup

And alongside the Ranunculus repens it looks as if you have bindweed too. A bit of thorough weeding coming up I think.

I have those in my yard too. Horrid plants. :(

Use Shreader MCPA it will kill creeping and tall buttercup. . My pasture was covered with with it. After 2 years it is about gone...