Despite the mounting evidence of efficacy of eHealth interventions, their mechanisms of action remain unknown. The current study analyzed patient log data as each patient engaged in an eHealth system called the Comprehensive Health Enhancement Support System (CHESS) and reports on how patients engage with different combinations of eHealth services over time. Newly diagnosed breast cancer patients (N = 443) were given access for 6 months to one of four different configurations of CHESS: (1) Information, (2) Information and Support, (3) Information, Support, and Coaching (Full CHESS), and (4) Full CHESS and Mentor. Besides a baseline survey, three follow-up posttests were administered. Action log data on how patients engaged with the CHESS were also collected and merged with surveys to examine how patients benefit during the cancer experience. The findings suggest that usage patterns were not competitive, implying that cancer patients’ access to more complex tools generates more use with their time spreading out over the diverse services. Despite overall decline in usage rates, it was less severe in Full CHESS and Mentor condition, suggesting that communication functions drive long-term engagement with the system. Notably, the strongest relation between use and cancer information competence appeared late in the follow-up period.