The detection of narrow and high-amplitude optical resonances in atomic cells is of crucial importance for the development of compact and high-stability lasers or vapor-cell optical references. In this work, using monochromatic light and appropriate polarization settings for the counterpropagating pump and probe beams, we demonstrate the detection of enhanced-absorption sub-Doppler resonances on the 𝐷1 line of the Rb atom. We report a theoretical model showing that the Zeeman coherence induced between magnetic sublevels—especially in the 𝐹 →𝐹′ =𝐹−1 systems, with 𝐹 and 𝐹′ being the hyperfine quantum numbers of the ground and excited states, respectively—plays a key role in the observed enhanced-absorption process. The theoretically predicted behavior matches the experimental observations well. The impact of light polarization, laser intensity, magnetic field, and cell temperature on the Doppler-free resonance features is experimentally investigated. For application, two identical diode lasers are frequency-stabilized onto enhanced-absorption sub-Doppler resonances. The fractional frequency stability of the laser beatnote is measured to be 1.8 ×10⁻¹² at 1 s and 8.4 ×10⁻¹² at 10⁴ s. These results demonstrate the potential of this scheme for the implementation of a compact or even chip-scale optical frequency reference, which might find applications in instrumentation, navigation, and metrology.