Understanding the initiation, propagation and evolution of water injection-induced fractures is essential for geo-energy applications. Hydromechanical stimulation experiments were conducted in a deep borehole drilled into crystalline bedrock to gain insights into these processes, involving simultaneous in-situ measurements of three-dimensional fracture displacements, injection flow rates, and water pressure in 2.4-m isolated borehole sections at 500-m depth. Three distinct sections were tested in the COSC-1 borehole (Sweden): a section of intact rock, a section with a hydraulically conductive fracture and a section with nonconductive fractures. Acoustic televiewer measurements conducted before and after the experiments confirmed the generation of new fractures. Accurate positioning of measurement tools was ensured through gamma log profiling and an innovative FFEC-based method for detecting flowing fractures. The tests revealed several transitional pressure values associated with mechanical events, with intact rock requiring the highest pressure to induce fracturing, followed by the nonconductive fracture section and the initially conductive fracture section. Following fluid injection, transient pressure decays were observed that were associated with leakage from newly generated fractures, providing insights into fracture behaviour under stimulation. Vertical displacements were predominant across the different tests, with measured displacements typically ranging from 10 to 100 µm. Fracture activation modes primarily involved the normal opening of subhorizontal fractures that were parallel to the metamorphic foliation, with some irreversible slip at higher pressures. However, a more complex scenario was observed in the test interval with previously nonconductive fractures, involving competition between the opening of subhorizontal fractures and reverse shearing of a steeply dipping fracture.