The result left the Belgians joint top of the group with seven points from three games along with Croatia, who came from behind to win 2-1 at fellow former Yugoslavs Macedonia.
Serbia, whose inexperienced team showed plenty of potential but also a lack of steel at the back, have four points from three games and now face a crunch visit to neighbours Macedonia on Tuesday.
The home side were punished for missing a hatful of chances when the score was level and after Belgium broke the deadlock against the run of play, Serbia struggled to keep up their momentum as the physically stronger visitors ran them ragged on a slippery turf in Red Star's stadium.
Captain Branislav Ivanovic, who had a tense personal battle with his Chelsea team-mate Eden Hazard, then failed to connect on Tosic's stinging low cross from the right which flashed across the face of goal.
Zeljko Brkic did well to keep out a Benteke effort from a tight angle at the other end moments later but was powerless in the 34th minute, when the Belgian striker headed Nacer Chadli's teasing cross from the right into the roof of the net.
Hazard should have made it 2-0 at the other end several minutes later, but Brkic did well to recover and palm away the midfielder's dinked shot after Chadli sent him clear with a defence-splitting pass.
Gaps in Serbia's tiring 4-2-3-1 formation began to open up as Belgian substitute Dries Mertens, who replaced Hazard, missed another chance for the visitors.
