Goalkeeper Matt Crothers said Castlemaine capitalised early, getting a couple of breakaway goals early.
He noted three goals were scored in the first half, including one inside the opening seven minutes.
He also pointed to “a few controversial offsides that went unnoticed”.
With several regular defenders unavailable, the Wanderers were forced to reshuffle.
“It wasn’t our usual backline, we had a few replacements,” Crothers said.
Despite the early setbacks, Deniliquin regrouped strongly after the break.
Their persistence paid off in the 75th minute, when Hamish Baker found the net to narrow the margin.
“We were able to come out firing in the second half; we had a lot more chances.
“Overall, we were pretty happy with the second half,” Crothers said, praising the lift in intensity and structure.
The result places the Wanderers fifth on the ladder, with a bye this weekend before they face the second‑placed Border Raiders on June 13.
“That will be a tough game, but we will look to do better, especially around our first half efforts.”