Automatic standpipe pressure control in drilling

A method of controlling standpipe pressure in a drilling operation can include comparing a measured standpipe pressure to a desired standpipe pressure, and automatically adjusting a choke in response to the comparing, thereby reducing a difference between the measured standpipe pressure and the desired standpipe pressure. A standpipe pressure control system for use in a drilling operation can include a controller which outputs an annulus pressure setpoint based on a comparison of a measured standpipe pressure to a desired standpipe pressure, and a choke which is automatically adjusted in response to the annulus pressure setpoint. A well system can include a standpipe line connected to a drill string in a wellbore, a sensor which measures pressure in the standpipe line, and a controller which outputs an annulus pressure setpoint based at least in part on a difference between the measured pressure and a desired standpipe pressure.