The Hawks' offence began to stall in the second and Auckland built a 10-point lead by halftime thanks to easy transition baskets.
"We just defended poorly, to give up 53 points in the first half is pretty ordinary," Downer said.
Guard Derone Raukawa (team-high 19 points, 5/8 three-pointers, four assists) sparked a comeback in the third quarter with the Hawks coming to life from behind the three-point arc, having struggled from deep early.
They trailed by just one point going into the final quarter before the wretched run Downer said left his team in too big a hole to recover from against a team as good as Auckland.
The coach said he and his team allowed themselves to be distracted by a few referee calls which went against them.
"Clunky" offensive possessions led to difficult shots and misses, he added.
"While we were frustrated, they just kept playing and ticking the scoreboard over and we didn't," Downer said.
"Every time it looked like we could get a little bit of momentum ... the next time down the floor they executed really well."
Downer thinks crisper passing and decision-making to create better shots will come as his team develops more chemistry over the season.
"I think a lot of it will just come down to attention to detail and being prepared to do the little things," he said.
"We'll just have to regroup. You can't fix everything, you've just gotta figure out how to put four good quarters of basketball together."
Auckland starters Dontae Russo-Nance, Chris Johnson, Siler Schneider and Rob Loe all scored more than 20 points in a balanced scoring effort while Johnson protected the rim with seven commanding blocks.
The Hawks are at home again for the visit of the Southland Sharks at 7.30pm on Thursday night.
