The result left Leipzig second on 57 points from 26 games, one behind Bayern who host VfB Stuttgart on Saturday after reaching the Champions League quarter-finals this week.
Leipzig dominated with crisp one-touch passing on a muddy pitch and missed a string of first-half chances before Austrian international Sabitzer struck the 46th-minute winner.
But the home keeper was powerless when a flowing move left Sabitzer with a simple tap-in from three metres as Dani Olmo squared a perfect pass from the right.
Striker Fabian Klos missed Arminia's best chance of an equaliser when he skied a shot from 12 metres inside the area before Nkunku drew a good save from Ortega at the other end.
Among Saturday's fixtures, third-placed Vfl Wolfsburg visit mid-table Werder Bremen, Eintracht Frankfurt in fourth host seventh-placed Union Berlin and Borussia Dortmund, who are fifth, travel to lowly Cologne.