Darren Edwards also had the luxury of being able to start three Wales Grand Slam winners - Dan Lydiate, Toby Faletau and Luke Charteris - but the formbook largely went out the window at Rodney Parade as Connacht did the double over the Welsh side.
Vainikolo's pair of tries - on 10 and 41 minutes - proved decisive with Connacht fly-half Miah Nikora exchanging five penalties to his opposite number Lewis Robling's four while Faletau's late try proving in vain for the hosts.
It had been the Dragons who took the lead when Connacht infringed at a maul and Robling slotted the resulting penalty although that would be the last time they had the lead.
The visitors, who had made much of the early running, moved the ball at speed to the left where Vainikolo skipped his way around the home defence to run in from 22m with Nikora converting.
After Robling reduced the deficit with a booming 50m effort, Kiwi stand-off Nikora soon got into his rhythm with three penalties inside 12 minutes, the last of which was after Lydiate was yellow carded by referee Giuseppe Vivarini for an offence at the breakdown.
Robling responded with two minutes remaining in the half when John Muldoon was pinged for holding on in the tackle but in truth the visitors were unlucky not to go in more than 19-9 ahead at half-time as they knocked on with the tryline begging.
They made amends though in the first play of the second half as Vainikolo relied on his power rather than his speed to put them 15 points ahead with Nikora unable to convert.
Nikora was off target with another penalty attempt and Robling edged the Dragons closer with a penalty of his own after Connacht failed to release the tackler.
After a 57th minute penalty from Nikora when the hosts were caught offside, the Dragons started to go for broke.
That approach started to pay dividends as Ronan Loughney was binned for persistent infringement and the Dragons did eventually cross the tryline with seven minutes to go through Faletau from close range.
But even though Eoghan Grace was also binned late on, the Dragons' revival was too little too late and they were left empty handed as they could not force even the consolation of a losing bonus point as Steffan Jones shanked a penalty wide.
|Newport Gwent Dragons Score Card|
|Connacht Rugby Score Card|