Syngenta trailed early on but led 2-1 at half-time thanks to srikes by Andy Rodgers and Kevin Fotheringham, before a second half collapse saw the visitors score three times.
“I thought we didn’t start the greatest in the first half then we got to grips with it,” said Diamond. "The boys grew into the game and we said to them at half-time: ‘Just continue what you’re doing for the second half’.
"But then we conceded a goal on 47 or 48 minutes and that set the tone for the rest of the afternoon. It was disappointing.
"It was probably self destructive, not Banks O’Dee carving us open. It was mistakes, individual errors that on another day the players wouldn’t do.
"All four goals they didn’t need to work for whereas we had to fight tooth and nail to get our goals.”
Second placed Syngenta face a vital East of Scotland League 1st Division Conference X clash at third placed Whitburn this Saturday.
"It is great for the league that the two teams are coming up against each other so early in the season,” Diamond added.
"We’re looking forward to it. We need to get our stall in order, we’re licking our wounds from a defeat.
"I know that Whitburn obviously lost again so the two teams want to right the errors of the previous weekend.
"It will make for a good game and hopefully we come out with the three points come 5 o’clock on the Saturday.”
Meanwhile, league leaders Bo’ness Athletic – who are above Syngenta on goal difference having played two games more – had a 4-3 home league win over Armadale on Friday night.
In front of a 325 crowd, Athletic prevailed thanks to a hat-trick by prolific striker Tiwi Daramola and a goal by midfielder Jonny Mitchell.
This Saturday, Athletic visit West Calder in the league.