With the words: "It's time for me to do something else, I think", Tua is gone from the ranks of the heavyweights and retired as New Zealand's leading modern boxer.
Alexander Ustinov might be 2.03m and 132kg and not the fastest boxer ever seen in the ring - but for Tua, it was like fighting a tree with a 2m jab.
Ranked 8th, 12th and 15th in the world respectively in three of boxing's four world bodies, Ustinov looked a formidable opponent as the two faced each other in the ring, the height and weight advantage crystal clear; Ustinov's waistband came up to Tua's chest.
He won a comfortable victory in the end, a unanimous points decision, in spite of a barnstorming Tua finish in the 12th round. By that time, Tua needed a knockout to win and was taking a punch from the big Belarusian to give on.
There was once another Ustinov - actor, writer and raconteur Peter Ustinov who said: "I imagine hell like this: Italian punctuality, German humour and English wine." David Tua might add another element to that - the 2m jab of Alexander Ustinov, the enormous 2.03m, 132kg heavyweight.
For those who watched the Tua fight with world heavyweight champion Lennox Lewis in 2000, the fight seemed disturbingly similar - Tua unable to breach the forbidding ramparts of the much bigger man, falling victim to a points lead and unable to connect with the fight-finishing punch.
It may be that, at 40, the Tua power has diminished. Or maybe he lost so much weight that it affected his power. Either way, the bombs never quite dropped - and when they did, Ustinov survived them.
A win would have meant Tua had a future at the top level - and the way he has prepared for this fight and the way he turned out for the bout was admirable.
This was no soft comeback. Ustinov is an awkward fighter for anyone and is the sort of boxer Tua has had problems with the past. His height makes him hard to tag on the chin and he is well used to shorter boxers banging away at the body; he has a well-developed guard. He is also a champion kickboxer and a decorated war hero in Russia's ill-fated Chechen campaign.
He is a better mover than might be expected for such a big man; no Michael Jackson, perhaps, but his ring movement is good and hand speed is enough to make that massive 2m jab and straight right difficult to slip and counter.
There was no secret about his tactics in this fight. Bear down on Tua, using his height and extended reach. The jab was ever-present, sometimes pawing but mostly faster than expected - and he hit and retreated, mostly circling away from the trademark Tua left.
In the first two rounds, probably won by Ustinov, the big man scored more with jabs while a patient Tua partially landed a looping left hook in the first and continued trying to find his range in the second. Tua did better in the third, upping the ante with a right to the body and one left-right combination that had the crowd on their feet and Ustinov clinching.
The fourth and fifth round re-established the early pattern - the big Belarusian jabbing and double-jabbing to score points; sometimes a double jab, sometimes the straight right. The punches were not hurting Tua, though they brought respect, his face marked by the heavy hands; Tua continued looking for an opening without landing much.
Ustinov was building up a big points lead and Tua's face was showing evidence of the impact of the Belarussian's jab and one right hand in the fifth round. At round six, the halfway mark, Ustinov probably had five rounds. Tua was busier in the seventh and eighth, hunting his man and moving forward - but was still facing a points deficit.
In the ninth, things began to change. Tua landed two lefts to the head - not the bone-crunchers of the past and, though Ustinov's head snapped back a little, he seemed to wear them well. The 10th saw Ustinov beginning to miss more and Tua finding his range better - but it was still Ustinov's fight to lose.
Tua stormed at him in the 12th, landing two good lefts - but it wasn't enough.
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Tua had been absent from the ring for two years and hasn't knocked anyone out for four. However, his last four fights were missing two things - Lee Parore as his trainer and Duco Events as his promoters and de facto managers.
In his slow decline from his 2009 comeback and triumphant return over Shane Cameron, Tua split from long-time promoter Cedric Kushner, managing himself and doing his own promotional work directly with Sky TV.
As is so often the case when boxers try to mix self-management and promotion with staying in the ring, it didn't work. Tua suffered a reverse when he drew with recent nemesis Monte Barrett in their first fight in the US, suffering the first knockdown in his career. He then turned up under-prepared and overweight for the return bout - which he lost even though he cracked Barrett's jaw and had him down right at the end of the fight.
The contrast between that period of Tua's boxing life and his fight with Ustinov last night was stark. Tua looked even slimmer than when he took on Cameron - even exciting comment that he might have lost too much weight and affected his power.
Whatever the truth of that, the sad fact is that the career of David Tua as a heavyweight boxer is now over.
In the other main attraction, light-heavyweight Robbie Berridge earned a TKO over Daniel McKinnon in a brawling, bloodied bout for the WBA-PABA and the WBO Oriental light-heavyweight titles.
In other bouts, Bubba Tuigamala, son of Inga, beat Wellington's Clint Foai by a TKO in round two, Australia's Lauryn Eagle won a unanimous points decision over Tauranga's Nicki Bigwood, Hamilton's light middleweight Cairo George won a unanimous decision over game Aucklander Ricky Campbell, Sam Rapira stopped Isaia Maku in the first round of their light-heavyweight bout and interesting 20-year-old light-heavy Nikolas Charalampous wore down Rico Chong Nee with a concentrated assault.
