Bruintjies took up athletics as a grade 1 schoolboy. In 2013, he was the South African under-23 champion in the 100 metres, defeating Akani Simbine in 10.44; at the national senior championships, he placed second behind Simon Magakwe in 10.58. He represented South Africa at the 2013 Summer Universiade in the 4 × 100 metres relay; the South African team placed seventh. In 2014, Bruintjies improved his personal best to 10.17 (+1.8 m/s) and ran the opening leg for South Africa's relay team at the Commonwealth Games in Glasgow; South Africa placed fourth in a national record 38.35. Bruintjies also competed in the 2014 African Championships, taking part in both the individual 100 metres and the 4 × 100 metres relay; in the individual event, he was eliminated in the semi-finals, while the South African relay team was disqualified in the heats.