Arniston slipped to their first defeat of the new season, finishing with nine men but having twice been in front with ten.
There were only five minutes played before Arnie’s David Jeffrey was given a straight red card for a hefty challenge on Jack Neave, which led to the latter being stretchered off.
Arniston’s 10 men battled with goalkeeper Dale Cornet in outstanding form.
Arnie broke the deadlock with the opening goal in 31 minutes through a fabulous finish from 20 yards by Danny Thomson.
Jock Landells’ men were pulled back to 1-1 in 36 minutes following a pacy run and finish by Kevin Millen.
In 53 minutes, Arniston were awarded a penalty, but Moffat’s effort was well saved by keeper Stewart.
Moffat made amends for that miss when he scored from a great pass by Thomson, but the lead only lasted three minutes as Millen beat the offside trap to score Downfield’s second equaliser.
In 87 minutes, a tiring home defence was outrun by substitute Ryan Kenneth who scored the winner.
Before the final whistle, Greig Callaghan was sraight red carded over arguing with the ref about a throw-in decision.
Arniston are away to Forfar West End on Saturday in the Premier League chasing their first win of the season in their third game .