Jahangir, World Open champion a record six times and British Open champion a record 10 times, announced on Monday that he would retire at the end of the season, but appeared to suffer a recurrence of the back injury that has kept him out of the game for six months.
'It looks like my last match but I want to speak to my father first,' Jahangir said. 'If it was left to me I would quit now. I suddenly felt I couldn't move in the third game because of the pain in my back. I can't keep playing at this level'.
Jahangir tired visibly from the third game onwards, suddenly shook hands at the end of the fourth and hurried off to the changing rooms. This left the score at 12-15, 13-15, 15-2, 15-7 and Marshall victorious.
Jahangir played with much of his old skill and some of his former pace for nearly an hour, during which the 21-year-old from Leicestershire rallied tenaciously to stay with him. 'I could tell from the second game onwards that he was tiring and that I might have a chance of winning,' Marshall said.
The young man also grew tense as the possibility of a sensation grew closer. Once Marshall accused Jahangir of blocking and was given a code of conduct warning for hurling his racket down in fury.
In the third game Jahangir slowed and offered little resistance. By the fourth he was holding his back. A no-let decision at 6-9 appeared to make him lose heart and after coming out of the door and offering his racket to the referee, the great man hardly contested the last handful of points at all.
'This is the best moment I have had in squash,' Marshall said. 'Jahangir is the best player who has ever lived and it has been my life's ambition to beat him. I thought he was invincible.'
Marshall now goes on to a quarter-final with the Australian-born Spanish qualifier Austin Adarraga, who won in straight games against the seventh-seeded former world champion Ross Norman.