The Mariners had not played since their October 2 win over the North Queensland Fury because of the FIFA international break and then a bye and were not at their best as the Roar moved to within three points of league leaders Adelaide United with a 2-0 win.
Arnold said it was clearly the fact his side hadn't played for so long that lead to the loss.
"We were rusty. We haven't played for 18 days. It's been a long break for us and I thought we played in fits and starts," said Arnold.
"For 15 minutes before half time I thought we looked like we were going to get back and the first 15 minutes after half time I thought we were probably the better side, but they've scored two freak goals.
"I was happy with the attitude of the boys. It was hard, we have another bye this weekend, that's our three gone and then we can get back into a rhythm because nothing replaces playing football.
"We're back on the training field working hard, get some injured players back because we had the bare minimum tonight.
"It's a long season, there's still 21 games to go its just one game, and there's plenty of time left."
The Mariners remained third on the table but fell four points behind the second-placed Roar.