Mechanisms of behavior change (MOBC) within Motivational Interviewing (MI) are thought to operate via both relational and technical elements. These elements are hypothesized to increase client motivation and self-efficacy for change and subsequently decrease drinking. Only partial support for this causal chain exists, particularly when using within-session change talk as the primary intervening variable. This study explored whether commitment to moderate or abstain from drinking and confidence to moderate drinking in the next day measured via ecological momentary assessment (EMA) provided alternative support for the theory. Data were from a pilot randomized controlled trial testing active ingredients of MI. Problem drinkers (N=89) seeking to moderate their drinking were randomly assigned to one of the three conditions: 1) MI; 2) Spirit only MI (SOMI), consisting of non-directive elements of MI, e.g., reflective listening; and 3) a non-therapy control. Participants completed daily EMA that measured confidence, both types of commitment, and drinks per day for a week prior to and during seven weeks of treatment. Hypotheses were not supported, and results were unexpected. Participants in SOMI were more likely to have higher daily confidence than those in MI; there were no condition differences for either type of commitment. All daily measures significantly predicted drinking; however, the MI group did not demonstrate a stronger relationship between the intervening variables and drinking, as hypothesized. Instead, participants in SOMI yielded the strongest relationship between daily commitment to abstain and drinking compared to the other two conditions. Multiple possible explanations for the unexpected findings are discussed.