Open-domain table QA requires reliable evidence localization beyond candidate retrieval. Compact table fingerprints reduce irrelevant signals during representation learning, but retrieval based on learned representations may still have limited ability to distinguish evidence segments among retrieved candidates. This issue is especially pronounced when tables are partitioned into segments that share similar metadata and schema patterns. We propose Probe-Grounded Reasoning (PGR), a coarse-to-fine framework for content-level evidence localization. PGR generates query-specific probes with metadata cues and cell-level evidence, then reranks candidate segments to improve fine-grained evidence localization. It then derives answers via a decoupled Semantic-Plan-Execute workflow with GRPO-optimized planning and execution. On Open-WikiTable, under a controlled evaluation setting with fixed BM25-retrieved candidates, PGR achieves 85.96% segment-level evidence accuracy at k=5 and reaches 69.0% end-to-end QA accuracy, suggesting that content-level verification supports more reliable evidence grounding for downstream reasoning. Code is available at https://github.com/XFastDataLab/PGR/.