The Azzurri only needed a point to be sure of a top-two finish in the section, but Luciano Spalletti's side impressed once again in a Nations League campaign that has seen them remain unbeaten heading into the final matchday at the weekend.
Some fine work down the right-hand side by Giovanni Di Lorenzo and Nicolo Barella opened up the Belgian defence just after the 10-minute mark, and the defender was able to tee up Tonali for a simple tap-in, with the Newcastle United man opening his account for the national side.
Domenico Tedesco's side threatened at spells in the second half, but Italy goalkeeper Gianluigi Donnarumma was equal to everything the Red Devils threw at him, keeping a first clean sheet in nine matches.
Italy soaked up much of the second-half pressure from the hosts, and were able to hit on the break at will, but squandered many chances to put the game to bed, with Mateo Retegui, Davide Frattesi, Di Lorenzo and Moise Kean all guilty of passing up promising opportunities.
That left the door open for Belgium to push for a leveller, and nobody came closer than Wout Faes, who struck the upright from a set piece with just over five minutes remaining.
Spalletti's troops survived the late onslaught though to earn a fourth win in five games in this group, and they will go into the final day three points clear of France at the top.
France's 0-0 draw at home to Israel tonight means that the winners of Group A2 will be decided when Italy host Didier Deschamps's side at San Siro on Sunday night, with the winners set to be seeded for the quarter-final draw.
BELGIUM VS. ITALY HIGHLIGHTS
Tonali goal vs. Belgium (11th min, Belgium 0-1 Italy)
Italy's early pressure pays off as a fine one-two between Di Lorenzo and Barella sees the marauding right centre-back thread the ball through the legs of Zeno Debast, handing Tonali the easiest of finishes for his first Azzurri goal.
MAN OF THE MATCH - ALESSANDRO BUONGIORNO
While Nicolo Rovella impressed on his international debut, and Donnarumma was on hand to keep Belgium at bay on more than one occasion, this could turn out to be a very important performance for Napoli's Alessandro Buongiorno, who has staked his claim to be a first-choice option going forward with a fine display tonight.
Up against his Napoli teammate Romelu Lukaku, Buongiorno did not allow the Belgium striker a moment's peace all night and kept the host's record goalscorer at bay all evening, helping to preserve Italy's clean sheet.
BELGIUM VS. ITALY MATCH STATS
Possession: Belgium 46% - 54% Italy
Shots: Belgium 11 - 11 Italy
Shots on target: Belgium 3 - 4 Italy
Corners: Belgium 7 - 1 Italy
Fouls: Belgium 8 - 9 Italy
BEST STATS
WHAT NEXT?
Italy welcome France to San Siro on Sunday night in an encounter that will decide who tops the section and will be seeded in the quarter-final draw, while Belgium will face Israel seeking to avoid a surprise relegation to League B.