Artificial intelligence (AI) tools, with their capacity to produce countless outputs from minimal input, continue to challenge and reshape creative workflows. While these developments support designers in various stages of the design process, there is growing interest in how designers integrate AI tools into their design processes, and how they engage with these tools in the conduct of designerly practices. This article investigates this topic through two consecutive studies. The first study involved a survey conducted among professional designers to understand which AI tools they use, their frequency of use, purposes of use, and self-reported proficiencies. The second study involved think-aloud interview sessions with 10 professional designers, each completing a design task specifically developed for this research using AI tools of their choice. Data from both studies were analyzed using the double-diamond design model as a framework. The findings reveal that AI tool usage is already prevalent among professional designers, extending across the entire design process and involving the coordinated use of multiple tools. These tools are used for a wide range of functions requiring analytical and synthesizing abilities in the exploration of the problem and solution spaces; prior experience and competences significantly shape AI tool usage. The findings also reveal that designers engage with these AI tools, displaying distinctive negative, neutral, or positive attitudes toward them, through different communication styles and interaction types.