Newton slotted home five penalties and two conversions for a total haul of 19 points in damp and slippery conditions at the Parc y Scarlets.
Neither side ever really got to grips with the weather but Scarlets emerged deserved victors after second-half tries from prop Rhys Thomas and winger Andy Fenby.
Both sides currently have 10 players away on international duty at the World Cup and it was the young fly half Newton, in the absence of both Stephen Jones and Rhys Priestland, who made the most of his opportunity.
His nerveless display with the boot kept the home side in touch in the first half as opposite man Naas Olivier, making his debut for Aironi, twice kicked the Italians into the lead.
But two Newton penalties either side of a sin bin for Aironi scrum-half Tito Tebaldi meant that the Welsh outfit went in at the break 9-6 ahead.
Aironi, still in search of their first ever away league win, were briefly back on level terms after the break when Olivier slotted over but in truth a 9-9 scoreline flattered the away side.
The Scarlets were dominant in the scrum and at the lineout and it only seemed like a matter of time before they finally strung enough passes together to cross the whitewash.
And on the 50-minute mark the try did come as a rumbling Ben Morgan run was held up just short of the line before the ball was recycled for prop Thomas to dive over in the corner, Newton adding the extras.
The right boot of Newton continued to keep the scoreboard ticking over as he added two more penalties to make it 22-9 with an hour gone.
And inside the last ten minutes Scarlets put the seal on the victory as Aironi full back Ruggero Trevisan was caught in possession and quick turnover ball put Fenby clear to touch down under the posts.
But there was still time for a late penalty from replacement fly half Rhys Jones as the Scarlets got their season off to a solid if unspectacular start.
|Scarlets Score Card|
|Rhys M. Thomas||1||5|
|Aironi Rugby Score Card|