With the rapid development of lithium batteries, energy storage and controlled nuclear fusion, the demand for lithium is increasing rapidly. Direct lithium extraction from unconventional brines (e.g., oilfield brines) is becoming increasingly critical. However, unlike traditional high Mg/Li salt lake brines, these systems typically contain high concentrations of calcium ions, which further increases the difficulty of lithium separation. To address these challenges, this study proposes two novel extraction systems that enable direct lithium extraction from brines with high concentrations of magnesium, calcium and sodium through a stepwise process. First, a triphenyl phosphate-tetraphenylborate synergistic system achieves 84% lithium recovery from simulated raw brine. By employing a strategy combining lithium stripping with in-situ precipitation of magnesium and calcium ions, the separation factors for Li/Mg and Li/Ca reach 178 and 1528, respectively. Single crystal structure analysis reveals the separation mechanism of lithium from magnesium and calcium by the organophosphorus extractant at the molecular level for the first time, and mass spectrometry analysis verifies the selective migration behavior of lithium ions during the extraction process. The resulting alkaline lithium solution is further treated with a novel diketone system, achieving a single-stage lithium extraction efficiency of 89% and a Li/Na separation factor of 415. The two-step strategy achieves an overall lithium recovery of 80% from raw brine, significantly higher than the conventional process. The obtained lithium carbonate is confirmed as battery-grade by XRD and composition analysis. This work provides molecular insights for designing novel lithium extractants and offers a new approach for direct lithium extraction from raw brines.