The Nerazzurri were unable to make the most of their superior possession as the Munich-born forward condemned them to their third consecutive match without a win.
Andrea Stramaccioni's side enjoyed the lion's share of possession throughout but failed to supply enough service to Diego Milito and Rodrigo Palacio up front, and an industrious Gialloblu were rewarded for their perseverance when Nicola Sansone belted in the game's only goal 15 minutes from time.
Winless in two, Inter needed a positive result to keep pace with those at the top of the league, but with just four minutes played it was clear that it would be no easy feat.
Aleandro Rosi charged forward and fed Marco Marchionni wide on the right, and, in attempting to intercept the cross, Walter Samuel inadvertently sent it towards his own goal. Fortunately for him, Samir Handanovic reacted well to keep it out and avoid an early disaster.
The Nerazzurri reacted positively and increased their ball retention in order to assert themselves on the game. After Ricardo Alvarez had been felled while on a scything run in the 13th minute, Fredy Guarin smashed a powerful shot from the resultant free kick, but it only found the side netting.
The visitors were unable to make the most of their superior possession, and Handanovic was again tested with 32 minutes played. Amauri ran across his defender to meet a cross but his powerful header was straight at the keeper, who palmed the ball to safety.
Inter's string of corners finally created a clear-cut chance when Guarin's deep delivery was sent back into the middle by Andrea Ranocchia, and an unmarked Esteban Cambiasso was unable to steer his header past Antonio Mirante.
In the 63rd minute it could well have been the Nerazzurri, but once more Mirante made an impressive save. Guarin was the source one more, but his ferocious 30-yard piledriver was turned behind by the keeper.
The inability to create chances for Stramaccioni's men was punished finally punished in the 75th minute. Sansone, who had been quiet for much of the evening, surged into the Inter half and skipped past a weak tackle from Guarin before rifling an effort past Handanovic and into the bottom corner.
Defeat means the Milan-based club drops to fourth in the table - four points adrift of Serie A leader Juventus - while Parma rises to an impressive seventh place.