Diamanti scored 34 points in what was a season of two halves, with the league stopped in late March for a three-and-a-half month hiatus before resuming in mid July.
The charismatic Italian was followed in the voting by Sydney FC’s veteran Serbian midfielder Milos Ninkovic (28 points) – a previous Warren medallist – and Jamie Maclaren of Melbourne City, the league’s top scorer, who was awarded 25 points.
Perth Glory’s Diego Castro, the Spanish attacker who is also a previous Warren Medal winner and Mexican attacking midfielder Ulises Davila, of Wellington Phoenix, were tied in fourth place.
Another man who made a massive difference to his club – in his case turning them from serial under achievers into challengers in all competitions – was French veteran coach Erick Mombaerts.
The 65-year-old helmed Melbourne City to FFA Cup and grand final appearances – although they lost both – but also took City to their highest ever league position (second), their highest points total and led them to their first Asian Champions League qualification.
His performance was acknowledged when he was named Coach of the Year – a decision that will have surprised some, given Steve Corica, the Sydney coach, led his side to the Premiers Plate/Championship double having also won the title last season.
But Mombaerts’ 10 peers decided his achievements in transforming City during the interrupted season were more noteworthy than Corica’s efforts in keeping the Sydney ship on course. The votes were taken before the finals, so did not reflect Sydney’s defeat of City in the title decider, although previous coach of the year awards prove that not all championship winning mentors do get the award.
Mombaerts announced last week he was departing City and returning to France because of the coronavirus crisis and will be succeeded next season by Patrick Kisnorbo.
Riley McGree, from Adelaide United was named Young Footballer of the Year while Jake Hollman from Sydney FC was the Y-League Player of the Year.
City and Socceroos striker Maclaren was the Golden Boot Award winner after scoring 22 goals during the regular campaign.
Marco Tilio who was then with Sydney but is reportedly moving to Melbourne City was the top goal scorer for the Y-League 2019-20 season with nine goals.
Veteran centre back Nikolai Topor-Stanley from the Newcastle Jets is more used to stopping goals than scoring them. But his long range strike early in the round 21 game against Perth Glory sealed for him the A-League Goal of the Year Award.
Sydney shot stopper Andrew Redmayne collected the Hyundai A-League Goalkeeper of the Year Award for the first time while his team won the Fair Play Award after accruing the least number of yellow and red cards.
Chris Beath was Referee of the Year.
Michael Lynch is The Age’s chief soccer reporter and also reports on motor sport and horseracing