Balotelli, the former Manchester City, AC Milan and Liverpool forward, was well placed to score into an empty net in the 32nd minute from Jean Seri’s pass across goal after a surging run.
Four-time European champion Ajax levelled with Donny van de Beek’s goal in the 49th, and will be favoured to advance into the playoffs from the return game at home next Wednesday.
Celtic was held 0-0 at home to Rosenborg, and Dynamo Kyiv beat visiting Young Boys 3-1 in the Olympic Stadium which hosts the final next May.
In a thrilling Champions League debut, Istanbul Basaksehir trailed by two first-half goals at Bruges, led 3-2 in a fierce second-half spell, then conceded a 79th-minute leveler to draw 3-3.
Coach Gheorghe Hagi’s Viitorul Constanta won on its UEFA competition debut, as the first-time Romanian champion beat APOEL 1-0. Defender Cristian Ganea struck with a swerving left-footed free kick in the 75th minute.
Nine first-leg games Wednesday produced no away wins, and it was Astana 3, Legia Warsaw 1; Hapoel Beer-Sheva 2, Ludogorets Razgrad 0; Maribor 1, FH 0; and Salzburg 1, Rijeka 1.
Fifteen teams advance from the third qualifying round to join five more teams — including Liverpool, Sevilla and Napoli — in the playoffs next month