Flexible demand response (DR) resources can be leveraged to accommodate the stochasticity of some distributed energy resources. This paper develops an online learning approach that continuously estimates price sensitivities of residential DR participants and produces such price signals to the DR participants that ensure a desired level of DR capacity. The proposed learning approach incorporates the dispatch decisions on DR resources into the distributionally robust chance-constrained optimal power flow (OPF) framework. This integration is shown to adequately remunerate DR resources and co-optimize the dispatch of DR and conventional generation resources. The distributionally robust chance-constrained formulation only relies on empirical data acquired over time and makes no restrictive assumptions on the underlying distribution of the demand uncertainty. The distributional robustness also allows for robustifying the otpimal solution against systematically misestimating empirically learned parameters. The effectiveness of the proposed learning approach is shown via numerical experiments. The paper is accompanied by the code and data supplement released for public use. NOMENCLATURE Sets: N Set of nodes, indexed by i = {0, 1, . . . , n}, |N | = n + 1 =: m N + Set of nodes without the root node, i.e. N + = {N \0} L Set of edges/lines indexed by i ∈ N + G Set of controllable generators, G ⊆ N A i Set of ancestor nodes of node i C i Set of children nodes of node i T Set of time intervals, indexed by t Λ t Set of historic price signals at time t X t Set of historic demand response observations at time t Variables and Parameters: c i (·) Cost function of the generator at node ī d P i,t Active power demand forecast at node i at time t d Q i,t Reactive power demand forecast at node i at time t e Column vector of ones of appropriate dimensions f P i,t Active power flow on line i towards node i at time t f Q i,t Reactive power flow on line i towards node i at time t g P i,t Active power output at node i at time t g Q i,t Reactive power output at node i at time t g P,min i,t , g P,max i,t Minimum/Maximum active power output g Q,min i,t , g Q,max i,t Minimum/Maximum reactive power output sAuxiliary variable for distributionally robust chanceconstraints reformulation u i,t Voltage squared at node i at time t w i (x) Cost/discomfort of demand reduction x x i,t Active power demand reduction at node i at time tMapping of net-injections to line flows, R n×m C Auxiliary matrix (αe ⊤ − I) ∈ R m×m that maps ǫ into changes in nodal injections I Identity matrix of appropriate dimensions M Auxiliary matrix R m+1×m+1 of decision variablesApparent power on line i T i (α) Mapping of load error vector ǫ t to voltage change at node i as a function of vector α X i Reactance of line i X Auxiliary diagonal matrix diag[X i , ∀i ∈ N + ] ∈ R n×n α i,t Participation factor of the generator at node i at time t α t Auxiliary vector {α i,t , i ∈ N } ∈ R m×1 β iParameters of the price sensitivity model at node i,Ratio between the active and reactive powe...