Gerrard, netting his 40th European goal, struck from the spot after Ludogorets keeper Milan Borjan made a hash of a clearance and brought down defender Javi Manquillo.
Ludogorets went closest to a goal before the late flurry started when Roman Bezjak hit a post after 72 minutes.
It promised to be a memorable night for five-time former European champions Liverpool who were returning to the Champions League after a five year absence, but much of the match proved frustrating for them.
Ludogorets overcame a cautious start and began to stretch Liverpool at the back with Brazilian midfielder Marcelinho a constant menace with his swift breaks.
He was unlucky not to be awarded a penalty in the first half when Liverpool defender Dejan Lovren shoved him over, and he also went close to a goal himself in the second half.
But just as the game appeared to be petering out to a goalless draw, Balotelli struck for his first Liverpool goal since his transfer from AC Milan when he battled to win control of the ball and scored with his left foot.
With full time showing on the board, Younes Hamza played a ball through to Abalo who took advantage of a rash rush off his line by keeper Simon Mignolet, enabling the Spaniard to round the keeper and fire the equaliser into an empty net.