Powdery mildew caused by Erysiphe alphitoides is a persistent constraint on European oaks, yet the host responses in pedunculate oak (Quercus robur) that determine susceptibility or resistance remain poorly understood. We profiled transcriptomic changes at 30 hours post-inoculation in detached Q. robur leaves using RNA-seq, identifying 195 up- and 40 down-regulated genes. Up-regulated transcripts included receptor-like kinases (RLKs), ethylene-responsive factor (ERF)/ethylene components, calmodulin-like (CML) sensors, germin-like proteins, peroxidases, and phenylpropanoid pathway enzymes. Gene Ontology enrichment highlighted defense response and response to biotic stimulus, and Kyoto Encyclopedia of Genes and Genomes indicated plant–pathogen interaction. RT-qPCR experiments confirmed ERF017, mUCP5, CML37-like, and one of two CML19 prime targets. These data indicate the induction of RLK-linked, Ca²⁺/CML- and ethylene-associated defense response during early powdery mildew infection and suggest targeted time-course and functional tests of RLK/CML candidates.