Newcastle United midfielder Tonali tapped home his first international goal 10 minutes into a hard-fought win at the King Baudouin Stadium. The 24-year-old's strike was crucial as Italy were guaranteed a spot in the last eight with a draw either against the Red Devils or with France on Sunday night.
Italy lead France by three points at the top of Group A2 and will battle with Les Bleus for first place at the San Siro.
Italy are unbeaten since the Euros and only drew with Belgium last month after having to play over half the match in Rome with 10 men. Domenico Tedesco's Belgium meanwhile are six points behind second-placed France with one game remaining and cannot reach the quarters after winning only against Israel.
Romelu Lukaku wore the captain's armband in his first match for Belgium since their miserable Euros campaign ended in the last 16 to France.