Diamanti began his footballing career at the youth academy of A.C. Ciconia in late 2008, and was put on the A.C. Ciconia II team for the 2009-10 season. He performed well there, and was a proficient goalscorer in the Liga 2 Juliana, so in the summer of 2010 he was promoted to the main squad of A.C. Ciconia, where he has played since. In the Liga 1 Juliana, he has also become a proficient goalscorer and an important player for his team. Diamanti was the top goalscorer of the 2014-15 Liga 1 Juliana, with 23 goals.
In 2009 and 2010, Diamanti played for the Juliana national under-20 football team. In 2010, he made his debut for the senior Juliana national football team, although he did not become a regular player for the team until 2011. He has become a consistent and increasingly proficient goalscorer for his country, and as of 2015 he is considered one of the key forwards for the team, along with Erik Verbič.