The importance of harmony perception in understanding tonal melodies has been extensively studied, but underlying processes of implied harmonic perception remain unexplored. This study explores how listeners perceive implied harmony in real-time while hearing tonal melodies by addressing two questions: How is each tone of a tonal melody harmonically interpreted and integrated into the previous tones? How do harmonic expectations of “what” chord will follow and “when” the chord change will occur affect the processing? Participants with music training listened to tonal melodies and responded to target tones by singing their pitches as quickly as possible. The target tones implied an expected or an unexpected chord; they occurred at expected or unexpected times. The results showed that sing-back reaction times (RTs) were shorter for: 1) tones implying an expected chord; and 2) chord changes occurring at expected times, suggesting that harmonic expectations facilitate the processing of tonal melodies. Also, RTs became shorter over the presentation of successive target tones implying the same chord, suggesting that implied harmony becomes clearer as more tones belonging to a single chord are presented.