It is growing in bare areas of a poorly draining lawn.
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Another answer correctly identified it as speedwell, it is most prevalent in thin turf areas or gardens. Some good news is it reproduces and spreads only by seed. So depending on how much you have hand weeding is an option, it must be dealt with early in the season though before it flowers and goes to seed. The seed can lay dormant through the winter then sprout again come spring. Upper and lower leaves differ in appearance--a common characteristic of Veronica Spp.