The second-year coach was not happy about a questionable penalty awarded to the visiting side in the 57th minute, which left his side two goals down.
Not only was the contact between Southern United defender Tristan Prattley and Waitakere's Jake Butler questionable, it appeared to occur outside the box.
However, the linesman indicated it was a penalty and the referee promptly pointed to the spot. Southern United goalkeeper Tom Batty saved Butler's penalty, but Butler banged in the rebound to put his side in control of the match.
''I can't see what the penalty was for. I'm just completely confused by that,'' Fridge said.
''It was just two guys going for the ball; they seemed to roll together. The next thing the linesman has given it and the referee has pointed to the spot. I'm just baffled by it.
''That kind of changed the game. When it's only 1-0 you're still in it. But at 2-0 it gave them a bit of breathing space.''
The second goal came just moments after Southern United substitute Andrew Ridden almost knotted the game up with his left boot.
He was the home side's best player after coming for Andrew Mobberley early in the second spell, and showed it when he found space inside the box and fired just wide of the goal a few minutes after coming off the bench.
The home side looked a much better outfit after the halftime break, and even dominated possession and territory for chunks of the half.
It was encouraging after a sloppy first half in which the boys in blue did almost nothing but defend.
The season could not have started worse for Southern United after it went down 1-0 in the second minute of the match.
Waitakere's Aaron Scott scored the opener, but Southern United goalkeeper Tom Batty should have done better with his long-range attempt.
Scott fired from outside the box and it appeared Batty had tipped the ball over the bar. However, the ball fell into the back of the net.
''[Batty] said he should have got it,'' Fridge said.
''That was only after two minutes, so that was not a good start.''
Fridge was also ''disappointed'' by the lack of chances his team scored in the first half, and conceded his team was rusty after a lack of preseason matches.
Passes were not finding their target, while Waitakere consistently found space down the left-hand flank.
Southern United suffered a setback before the match, when Scottish striker Sam French was ruled out with an ankle injury.
But fellow Scottish forward Tom McBride looked good when he entered the game for Regan Coldicott in the 18th minute.
Despite the loss to highly-fancied Waitakere United, Fridge said there were positives to take from the match, particularly the much better second half performance.
''It's disappointing to lose the game, but there are still a lot of positives to take out of it,'' Fridge said.
''Once we iron a few things out, we will be fine.''
• The Southern United youth team hammered Manawatu 5-0 in Palmerston North yesterday to end its two-match losing streak in the national youth league.
• Football South is still winless in the women's national league after losing to bottom-of-the-table Capital Football 4-1 in Wellington yesterday.
