Osman won the 1961 presidential election by a single decisive vote.

Evidence

The results of the first ballot were announced at 10:15 a.m. Each candidate received sixty votes, and one vote was disqualified as it was not decipherable. In the second round, Sheikh Ali advanced by two votes. Once this was pronounced, many thought Sheikh Ali would win the last and final round. Here is how the American embassy observers described it: … [On the second ballot] Sheikh Ali Giumale improved his position and obtained 61 to 59 for Aden Abdulla, one vote again being illegible. It was thought that Sheikh Ali Giumale would now go on to victory but on the third and final ballot, there was a slight shift in the sentiment and Aden Abdulla received 62 votes to 59 for Sheikh Ali Giumale after it was finally decided the deputy with the indecipherable handwriting was actually voting for Aden Abdulla. — Abdi Ismail Samatar, Africa’s First Democrats, 595