Tiny weed

In our lawn. I call it trefoil but not sure how correct that is. It probaly came in some plants from a nursery and transferred to the lawn over time.
The lawn is already very brown. We don't bother watering it but around the edges where the irrigation seeps on to the lawn it is quite green from this weed and it's tiny tiny flower.I lay on the lawn with camera on wheat bag and the 10+ macro filter.

Thanks to Osuzanna for hosting Tiny Tuesday.