Owen followed his brother Gary into professional snooker in 1973, entering the 1974 World Championship. As an unknown quantity, Marcus was not expected to progress far; however, he beat Dennis Taylor and Maurice Parkin to set up a last-16 meeting with Gary. Gary held Marcus to 5–5 at one point, but could not prevent him from pulling away to reach the quarter-final with a 15–8 victory. There, Marcus faced Ray Reardon, but having recovered from 3–9 to 7–9, was eventually defeated 11–15.