Having recalled Balotelli to the Italy squad for the first time since the 2014 World Cup, Mancini - instilled as boss on 14 May - showed no hesitation in starting his former Inter and Manchester City prodigy as the spearhead in a relatively inexperienced line-up.
And Balotelli duly repaid Mancini's faith, capping his first start since the 1-0 defeat to Uruguay on June 24, 2014, with a sublime solo strike 21 minutes into Monday's clash in St. Gallen.
Unlike the Azzurri, Saudi Arabia have qualified for this year's World Cup, up against Egypt, Uruguay and hosts Russia in Group A, but Juan Antonio Pizzi's side were lacklustre throughout - Domenico Criscito hitting the woodwork as Italy pressed for a second.
Balotelli made way to a standing ovation just before the hour, and that change proved decisive when substitute Andrea Belotti drilled in Italy's second on 68 minutes.
Sloppy play from Davide Zappacosta enabled Yahya Al Shehri to pull one back for Saudi Arabia, but Italy - thanks to a great stop from Gianluigi Donnarumma - held firm to get Mancini's tenure off to a winning start.
26 - Tonight's starting XI is the youngest fielded by Italy since November 2010: average age is 26 years 8 days. Fresh.— OptaPaolo (@OptaPaolo) May 28, 2018
Balotelli had the ball in the net inside two minutes, having capitalised on Mohammed Al Owais' dreadful clearance, but Italy's celebrations were cut short by the offside flag.
Italy's striker looked in the mood, and - after going close with a powerful header - turned a sublime pass into Alessandro Florenzi, who failed to apply the finish after rounding Al Owais.
But Balotelli did not have to wait long to get on the scoresheet, the 27-year-old twisting and turning his way clear of three defenders before thumping an unerring finish into the bottom-left corner from 25 yards out - his first international strike since netting against England four years ago.
Saudi Arabia offered little attacking threat, and Italy were just inches away from extending their lead when Criscito's venomous strike rattled the crossbar.
Salem Al Dawsari's introduction gave Saudi Arabia some impetus after the restart, though Lorenzo Pellegrini squandered a great chance to put the result beyond all doubt when he scooped over from Zappacosta's cross.
Balotelli's impressive return came to an end on 58 minutes, and the substitution soon proved another masterstroke from Mancini as Belotti made his case for a starting berth.
Having seen his initial header well saved, the Torino forward followed up the rebound, lashing in from point-blank range.
Lorenzo Insigne drew a fine save from Al Owais as Italy threatened to run riot, but the Azzurri's lead was reduced with 18 minutes remaining.
Zappacosta's slip allowed Al Dawsari to pounce and feed Al Shehri, who got the better of the onrushing Donnarumma before prodding home into an empty net.
Donnarumma was Italy's hero late on, though, AC Milan's youngster brilliantly keeping out Fahad Al Muwallad's close-range strike to ensure Italy claimed victory.