United had a great chance to try and wrestle second spot off the Mariners but faltered when it mattered and went down to end any hope of gaining a top-two finish.
Bleiberg said it was a disappointing result but was delighted his side were again in the A-League finals.
"The Mariners were very good and they're second on the ladder for a reason," he said.
"It hurts to lose such an important game but there is nobody to blame and we just have to cop it on the chin. We have to learn from it and refresh ourselves as best we can to prepare for Saturday's game.
"On the positive side, we are in the Finals for the second year running and we are only two years old, so we still have a lot to be proud of."