The influential fly-half surpassed Ronan O’Gara’s all-time tally of 1,083 in style with the fourth of his side’s eight tries on a balmy evening at Stade de la Beaujoire.
Captain Sexton also kicked a penalty and four conversions en route to moving on to a career total of 1,090 before being withdrawn from a bruising Pool B encounter at half-time ahead of next week’s crucial clash with South Africa.
Tries from Tadhg Beirne, Caelan Doris and Mack Hansen paved the way to victory, with Bundee Aki’s double and second-half scores from James Lowe and Rob Herring capping Sexton’s landmark moment.
Vaea Fifita crossed just before half-time to give Tonga hope in the aftermath of Peter O’Mahony’s yellow card, while William Havili contributed three penalties and a conversion.
But the world’s top-ranked nation comfortably maintained their 100 per cent start to the tournament and emerged relatively unscathed moving towards pivotal Paris appointments with the Springboks and Scotland.
Despite the looming threat of the reigning world champions, head coach Andy Farrell named an extremely strong starting XV showing just four personnel changes from last weekend’s thumping 12-try triumph over Romania.
His side, unfamiliar in white shirts, were once again heavily backed on the terraces and met Tonga’s Sipi Tau by taking a collective step forwards.
Sexton slotted an early penalty to increase the volume, but Havili landed a long-range reply to level before Ireland were frustrated to have an Andrew Porter try disallowed for a knock-on by Hansen.
The disappointment proved to be fleeting as Farrell’s men remained on the front foot, culminating in Beirne collecting Doris’ pass and touching down under the posts for his third score of the tournament.
Havili landed another audacious penalty from close to halfway to cut Tonga’s deficit, but their hopes of a first win over the Six Nations champions were swiftly reduced by costly indiscipline.
Lowe was clattered in his own 22 by opposing wing Solomone Kata, gifting Ireland a penalty at the other end of the field from which Doris powered over.
Hansen - one of four men recalled by Farrell - then superbly danced through the opposition defence wide on the right to stretch the scoreboard, leading to Sexton equalling O’Gara’s previous national record.
Sexton overtook his former fly-half rival in memorable fashion to secure the bonus point.
The evergreen 38-year-old rolled back the years by effortlessly slipping through Tonga’s defence to touch down and then celebrated jubilantly with fans seated behind the posts, before regaining his composure to add a simple conversion.
Ireland were threatening to blitz the stunned underdogs.
Yet Tonga roared back and, during a series of penalties close to the Irish line, O’Mahony was sin-binned before former All Black Fifita shrugged off an early injury issue to power over.
Ireland changed their entire front row at the break, while wrapping Sexton in cotton wool.
Yet replacement tighthead prop Finlay Bealham departed for a head injury assessment after Havili kicked his third penalty of the evening, requiring the swift return of Tahdg Furlong, before substitute hooker Herring had a try chalked off on review.
Lowe eventually claimed Ireland’s fifth and official man-on-the-match Aki then propelled himself to the top of the tournament’s embryonic try-scoring charts with a quick-fire brace, both converted by Sexton’s replacement Ross Byrne.
Ireland were relatively untroubled in the second period and Herring sealed another statement win - a 15th in succession overall - ahead of two critical fixtures in the French capital.