German Denis scored twice to inspire Atalanta to a 3-2 win over Internazionale at the Stadio Atleti Azzurri d'Italiato, and see them climb to sixth place in Serie A.
Stefano Colantuono's side took the lead in the ninth minute through Giacomo Bonaventura's header, but Inter levelled eleven minutes into the second half from a thunderous Fredy Guarin free-kick.
Denis tapped in on the hour to put the home side ahead again, then the Argentinian extended Atalanta's lead seven minutes later from the penalty spot.
Rodrigo Palacio pulled one back for Inter with six minutes to go, but in a frenetic finale that saw Atalanta substitute Facundo Passa receive a red card, the visitors were unable to force an equaliser.
The defeat is the first Internazionale have suffered away from the Giuseppe Meazza in Serie A this season, and brings to an end their ten match-winning run in all competitions.
Atalanta opened the scoring in the ninth minute with their first effort on the Inter goal. Federico Peluso crossed from the left, and Bonaventura timed his run past Matias Silvestre perfectly to head the ball firmly beyond goalkeeper Samir Handanovic.
Inter had a great chance to level in the 20th minute when Silvestre's header from a corner arrowed straight to Palacio, but Atalanta goalkeeper Andrea Consigli brilliantly blocked the Argentinian's point-blank header.
Inter seemed to be really struggling with the pace of the Atalanta counter-attacks, and Stefano Colantuono's side should have doubled their lead in the 33rd minute, after another fine move down the flanks.
Bonaventura found Ezequiel Schelotto down the right and his cross dropped perfectly for the unmarked Denis six yards out, but the Argentinian got it all wrong and scooped his shot over the crossbar.
Atalanta goalkeeper Consigli then made another superb close-range block in the 39th minute as he reacted quickly to Cassano's chipped cross from the edge of the area, and threw himself in front of Palacio to save.
Internazionale levelled on 56 minutes in emphatic fashion. Federico brought down Guarin on the edge of the area, and the Colombian took the free-kick himself and cracked the ball into the top hand corner of Consigli's goal.
Denis then made up for the embarrassment of his earlier miss when he gave Atalanta the lead for the second time on the hour. Juan Jesus's attempt to clear the ball only picked out Schelotto, who superbly put in Maxi Moralez down the right hand side of the area to cross for his strike partner to sweep home from close range.
Six minutes later, Atalanta extended their lead after the hapless Silvestre lunged into Moralez on the right-hand side of the area and conceded a penalty, which Denis coolly slotted to the left of Handanovic.
The home side could have wrapped up the game in the 82nd minute, when Schelotto cut the ball in from the right to Parra, but Handanovic made a superb save low to his right.
Two minutes later, the visitors pulled one back, when Guarin played a ball from the edge of the area inside Atalanta defender Guglielmo Stendardo, and Palacio lashed a left-foot shot past Consigli.
Parra lost his discipline in injury-time as Inter bombarded the Atalanta goal, and was sent off after an elbow to Guarin. But the Bergamo side held on for their first win over Internazionale since 2009.