The Scots led 33-3 with 10 minutes left, but the Azzurri avoided a morale-sapping thrashing with three late tries.
Edinburgh wing Kinghorn scored twice in the first half and once after the interval to bridge a three decade gap back to March 4, 1989, when Iwan Tukalo claimed three tries in a Five Nations win over Ireland at Murrayfield.
Fullback Stuart Hogg and replacement centre Chris Harris also crossed as Scotland won a seventh successive home game in the Six Nations, their longest such run in the championship since 1975.
"We took our chances when they were available and it was brilliant to get a couple of tries out of it," Kinghorn told the BBC.
Reigning champions Ireland are sure to pose a sterner test next Saturday but coach Gregor Townsend had reason to be happy with a seventh successive Scottish victory against Italy, who line up against Wales in Rome next Saturday looking to end a record run of 18 successive defeats in the Six Nations.
Italy coach Conor O'Shea and captain Sergio Parisse, making a record 66th Six Nations appearance, were left pondering what might have been after scrumhalf Guglielmo Palazzani and wings Edoardo Padovani and Angelo Esposito all scored tries in a late attacking flurry.
"Against quality opposition like Ireland, we can't release a Test match like that," said Townsend. "We were well in control and just gave Italy momentum by being less aggressive and slipping off tackles."
Meanwhile outstanding No 8 Parisse said Italy had left it too late to turn the tide of the match.
"With possession we are dangerous and can score tries but Scotland deserved the win," he insisted. "We let Scotland have too much possession in the first half at this level."
O'Shea was forced to change his starting XV before kick-off, injured scrumhalf Tito Tebaldi making way for Palazzani and his team were on the back foot from the start of a one-sided opening half.
A chip and chase up the right wing would have earned Scotland a second minute try had Italy fullback Jayden Hayward not rushed across to hack the ball into touch.
Grant Gilchrist thought he had scored from the ensuing catch and drive but television match official Simon McDowell ruled the lock had made a double movement in touching down.
Kinghorn and Stuart Hogg also stretched Italy's defence but it was the visitors who scored first, former Scotland Under-20 international Tommaso Allan landing a ninth minute penalty.
Two minutes later, though, Scotland flyhalf Finn Russell angled a perfectly judged chip kick into the arms of Kinghorn, affording the left wing a clear run to the line from 22 metres out.
Scotland captain Greig Laidlaw pushed the conversion wide but the Clermont scrum-half atoned for the miss by adding the extras to a superb Kinghorn try midway through the first half.
Josh Strauss and Laidlaw smartly switched the direction of an attack, with Kinghorn going over in the left corner after Russell, debutant centre Sam Johnson and Hogg combined in a slick handling move.
Six minutes into the second half, Scotland were into the comfort zone with a third try, Russell stabbing a kick through for Hogg to beat Esposito to the touch down with his outstretched left hand. Laidlaw's conversion made it 19-3.
Kinghorn's hat-trick came in the 53rd minute when he cut through the Italian defence from 15 metres after a break by flanker Jamie Ritchie.
Laidlaw again converted. Then, Ali Price having replaced the Scotland skipper, Russell landed the conversion after Harris burst over in the 61st minute for his first international try.
At that stage Scotland were on course for a rout at 30 points ahead but, with Simon Berghan sin-binned, they took their foot off the pedal in the last 10 minutes.
Palazzani, Padovani and finally Esposito all exploited lax defending to apply a belated Italy gloss to the scoreline.