The Orcas again scored twice after the break to appear to set themselves up at 28-16, but the Mustangs kept plugging away, getting an unconverted try to narrow the gap to two points with time running out.
They attacked from the kickoff to reach the Orcas tryline, but the final pass was just over the receivers head as the fulltime whistle sounded.
Boxon winger Emitai Logadraudrau scored two of his team's five tries, while clubmate Shade Heta got another while playing the full 80 minutes at prop.
Centre Tautahi Rawiri added three conversions.
"It was a great game to watch," said Reweti, adding he hoped the effort in front of several ex-players from Palmerston North would give them "itchy feet" and be a boost for the MRL, who had to fold their Premier grade this year through lack of teams.
"The boys, I think, through the game their confidence grew.
"We just fell short."
The Mustangs will now play their second NZRL National Championship match against the Taranaki Sharks in New Plymouth this Saturday, and Reweti will see how the squad is trucking at training before deciding on any changes to the current 18.
"There's a lot for us to work on, defensively."