The Alan Hunt-coached Stags were again exposed in the bowling and batting amid some eyebrows raised on how undercooked veteran Jacob Oram got into the line-up ahead of Andrew Mathieson.
If experience was a factor then it certainly didn't materialise on the field.
"Look, Jake didn't get too many runs [four] and didn't do too well with the ball either.
"But he can be a match-winner on his day. But he buggers off to Bangladesh now and we won't see him until March," Sinclair said.
He said CD just weren't good enough last night but now needed to put things right by going out to clinch the four-day Plunket Shield as well as retain their domestic one-day Ford Trophy.
Yesterday's defeat equates to "a lack of momentum" going into the resumption of the Plunket Shield next week in Napier.
"We have to do a bit of soul searching because rightly or wrongly, we played poorly so we have to send a report to the CD board to say what went wrong."
The former Black Cap said perhaps CD needed to minimise its focus on the Shield and Trophy campaign to concentrate on the HRV Cup as other associations were.
"No one seems to give a stuff about first-class and one-day competitions.
"That's what it all seems to be about - putting money in the coffers.
"Is that where we want cricket to be going looking at the performance of our test cricket in South Africa?" he asked.
Yesterday, CD, with captain Kieran Noema-Barnett winning the toss, accumulated 132-7 from a rain-shortened 18 overs.
The umpires stopped play in the 12th over with CD at 79-3 which would have had Auckland coach Paul Strang and captain Gareth Hopkins threading their worry beads.
Sinclair again showed he was the best CD investment this summer with 44 runs from 40 balls, including six fours.
Fellow opener Jamie How made 19 from 14 balls, including two lusty sixes and a four, but No3 Jeet Raval finished the T20 campaign with a diamond duck after Michael Bates and Anaru Kitchen combined to run him out without facing a ball.
Ben Smith got 15 from as many balls and first-class grafter Carl Cachopa backed up with 25 runs from 15 balls, including two boundaries and a six, before Bates rattled his stumps.
Bevan Small and Tarun Nethula contributed nine each.
Bates was the Aces' pick of bowlers, claiming 23-1 from four overs, while Andre Adams took 2-31 and opener
Matt Quinn got 1-35.
The hosts showed immense discipline, gifting only four extras, including a wide.
It didn't start too well for CD in defending the target with Zimbabwe international Kyle Jarvis tidy with 10 runs from two overs but fellow opener Small going for 19 runs off one.
The Aces whittled down the asking rate of a shade under eight runs an over to 5.41 runs an over with an over to go.
Oram also joined the rash of failed death bowlers, going for 17 runs in the 16th over while Jarvis went for 12 off his third and the game's penultimate over.
Spinner Marty Kain was outstanding with 2-18 from four overs while Nethula was equally frugal with 0-26 from four.
Small did well to finish with 2-26 from three and Jarvis 0-22 from three. Oram was 0-42 from three and CD gifted four wides.
Auckland opener Lou Vincent scored an unbeaten 52 from 39 balls while South African import Donovan Grobbelaar added 36 from 19.
The Aucklanders, even after Kitchen retiring hurt, booked a semifinal berth against the Wellington Firebirds at the Basin Reserve in the capital city this Friday to decide who will earn the right to face table-topping Otago Volts at
the University Oval, Dunedin, in the final on Sunday with Australian speed merchant Brett Lee at their disposal as a late signing.
