Opportunity management offers the possibility of increasing the chances of achieving the project objectives. In construction projects, some opportunities may be associated with quality improvement, whereas others may lead to time and cost savings. Opportunities leading to savings may be beneficial for one contracting party and disadvantageous for other project stakeholders. An unbalanced distribution of benefits from opportunities, sometimes coupled with negative effects, can arise from opportunistic behaviours. Much is known about opportunism in the context of project management. Although the link between opportunism in projects and opportunity management is evident, extant literature does not explicitly bridge these two aspects of project management practice. This paper is conceptual, and its purpose is to broaden the view on opportunity management in construction projects by emphasising that the implementation of some opportunities may be associated with opportunism. This paper summarises realistic examples of certain opportunities arising from opportunism. These examples show that some opportunities favouring one party can trigger negative effects that compromise the needs of various project stakeholders such as clients, end users, and project owners of current and future expansion projects. The perspective on opportunity management from the lens of opportunism helps clients recognise possible hidden agendas of contractors striving to optimise design solutions and ease project execution. Understanding the opportunistic nature of certain opportunities proposed by internal project team members can prevent clients from exploiting such opportunities. Since it is impossible to eradicate opportunism in construction projects, clients need to be prepared to deal with opportunism before it becomes a matter of concern. Thus, the early involvement of knowledgeable project members capable of flagging the presence of antecedents of opportunism is beneficial for clients.