Top seed Grigor Dimitrov suffered a shock exit to wildcard Malek Jaziri in the opening round of the Dubai Duty Free Championships.
The Bulgarian took a first set lead but Jaziri, ranked 117th in the world rankings, rallied back against the world number four to win 4-6, 7-5, 6-4.
The win sees the Tunisian, 34, secure the biggest win of his career to date.
Dimitrov reached the Rotterdam Open final a week ago, but admitted he has recently been struggling with illness.
Number two seed Lucas Pouille suffered no such hiccups as he beat Latvia's Ernests Gulbis in straight sets to advance.