The Argentine netted the opening goal of the first leg, his 57th this season, but it was Ibrahimovic who had the last word as he set up a late equalizer.
Jahn, who came on as a substitute in the 66th minute because forwards Alan Gordon and Steven Lenhart were injured, came up with the equalizer in his second MLS appearance.
But Diego Forlan pulled one back after 71 minutes -- incredibly Inter's first in 541 minutes -- before the Uruguayan set up Diego Milito for the equalizer.