  We elucidate the relation between Painlev\'e equations and four-dimensional
rank one ${\cal N= 2}$ theories by identifying the connection associated to
Painlev\'e isomonodromic problems with the oper limit of the flat connection of
the Hitchin system associated to gauge theories and by studying the
corresponding renormalisation group flow. Based on this correspondence we
provide long-distance expansions at various canonical rays for all Painlev\'e
functions in terms of magnetic and dyonic Nekrasov partition functions for
${\cal N= 2}$ SQCD and Argyres-Douglas theories at self-dual Omega background
$\epsilon_1+\epsilon_2= 0$, or equivalently in terms of $c= 1$ irregular
conformal blocks.
