All Tennis Players How Many Grand Slams Has Harold Mahony Won? Harold Segerson Mahony (13 February 1867 – 27 June 1905) was a Scottish-born tennis player.Harold Mahony has won 1 Grand Slam. FacebookTwitterEmail How Many Grand Slams Has Madison Keys Won? How Many Grand Slams Has Jannik Sinner Won? How Many Majors Has John Isner Won?