DNA methylation is an epigenetic modification involved in cancer. The clinically approved nucleoside DNA methyltransferase (DNMT) inhibitors 5-azacytidine and 5-aza-2′-deoxycytidine lack selectivity and stability, resulting in high toxicity. Previously, we discovered 3-halo-3-nitroflavanones as non-nucleoside DNMT inhibitors. Here, we designed and synthesized a new series of 2-substituted haloflavanones to increase compound chemical stability. Moreover, replacement of the nitro by an additional halogen enhanced compound potency. Indeed, compound 34b (anti-3-bromo-3-chloro-2-methoxyflavanone) exhibited submicromolar DNMT3A inhibitory activity, upregulated the expression of DNMT-targeted genes, and impaired cell proliferation. Importantly, 34b triggered a critical cell cycle arrest in the G1/S transition, notably in p53-depleted HCT-116 colorectal cancer cells, which paves the way for novel therapeutic opportunities. 34b competes for the same DNMT catalytic pocket as confirmed by saturation transfer difference-nuclear magnetic resonance, but assuming different docking poses as shown by computational studies. Overall, the high stability and activity of 34b make it a promising DNMT inhibitor for anticancer research and therapy.