usually see the first-arriving left-turner yield in practice as well, since I encounter an occasion like this regularly. Maybe the law is different in UT since so many say first-come first-serve.

(1) The driver of a vehicle intending to turn to the left within an intersection or into an alley, private road, or driveway shall yield the right-of-way to any vehicle approaching from the opposite direction which is within the intersection or so close thereto as to constitute an immediate hazard.