  High-temperature superconductivity emerges in the CuO$_2$ plane upon doping a
Mott insulator. To ascertain the influence of Mott physics plus short-range
correlations, we solve a three-band copper-oxide model in the charge-transfer
regime using cellular dynamical mean-field theory with continuous-time quantum
Monte Carlo as an impurity solver. We report the normal and superconducting
phase diagram of this model as a function of doping, interaction strength and
temperature. Upon hole doping of the charge-transfer insulator, the phase
boundary between pseudogap and correlated metal consists of a first-order
transition line at finite doping ending at a critical point, as in the one-band
model. Beyond the endpoint, the phase boundary continues as a Widom crossover
line, across which thermodynamic quantities peak. This phase boundary
determines changes in the pairing mechanism and is an emergent phenomenon
characteristic of doped Mott insulators, independent of many microscopic
details. Broader implications are discussed.
