Higher-order thinking skills (HOTS) mathematical problem-solving was first introduced in the Form-3 assessment (PT3) in 2014. However, to date, there have been no studies of students' ability to solve the mathematical problems in this assessment. Therefore, this study investigated the emerging patterns and problems of HOTS mathematical problem-solving in the PT3. This investigation was a case study and classified under a qualitative research approach. Oral reporting (i.e. thinking aloud protocol) was used to obtain the data. The participants were 10 Form-3 students who were candidates for PT3 in 2015. They were students in a secondary school in a district in Johor Bahru. The results show that students who successfully solved the HOTS mathematical problems produced the same process starting with understanding, followed by phases of planning, implementation, and ending with the final answer. The students who failed to answer the HOTS mathematics questions produced a solution pattern starting with understanding followed by planning and implementation. Based on the patterns, this study also identified the problems that emerged in every step of the HOTS mathematical problems-solving processes and discusses how they could be overcome and improved.