The Magpies had a man sent off after just 11 minutes when Mark Yeates was shown a straight red card for a challenge on Ricardo Almeida Santos.
John Akinde then thought he should have had a penalty minutes later when he appeared to be hauled down by Notts goalkeeper Adam Collin, only to be booked for simulation.
Although at a disadvantage, Notts managed to create chances with Marc Bola going close on two occasions from distance.
But the breakthrough eventually arrived in the second half when Jorge Grant teed up Tootle, who lashed a superb finish past Benjamin Buchel.
Barnet fought back in a bid to claim an equaliser and should have levelled when substitute Ruben Bover Izquierdo blazed over from eight yards.
With the game stretched, Grant could have got himself on the scoresheet when he raced onto a fine Shola Ameobi pass, but he curled wide.