The Brazilian struck on 31 minutes to hand Delio Rossi a slender defeat in his first game in charge. The 52-year-old had replaced the sacked Ciro Ferrara on Monday, but Rossi's former club ensured that it's now just one point in four games for the Blucerchiati.
Lazio were without injured pair Ederson and Tommaso Rocchi. Antonio Candreva sat out a suspension and Mauro Zarate was left in Rome after his latest strop. The troubled forward looks to have played his last game for the club. Andre Dias returned in defence in place of Michael Ciani.
Sampdoria pegged the visitors back during the opening quarter of an hour. Federico Marchetti was called into action to push an Icardi shot around the post and tip a fine Eder volley over, after the frontman had played a neat one-two. Giuseppe Biava put himself in the way to block Eder's shot after a mazy run.
Lazio fashioned their first chance on 19 minutes, when Senad Lulic fired over. The Bosnian turned provider when he ran to the byline and pulled the ball back across the face of the goal. Sergio Romero pushed it clear and Hernanes shot through a sea of bodies to find the bottom corner.
Biava dragged Eder down, but the forward wasted a free-kick by firing low into the Lazio wall. Romero gathered a weak Hernanes set piece, before Daniele Gastaldello spurned a good chance to equalise on the stroke of half time. The Sampdoria captain was unmarked to meet a corner, but couldn't direct his header toward goal.
Roberto Soriano presented Cristian Ledesma with an early Christmas present courtesy of his stud marks on the elbow. The substitute had been on the pitch less than 30 seconds before catching Ledesma as he ran past him. The midfielder was treated on the sidelines and alright to continue.
Abdoulay Konko shot high, and Dias headed over before Lazio retreated. Every time Sampdoria ventured forward they were met by a sea of dark Blue as the Eagles snuffed out each attack.
Nicola Pozzi came closest to finding an equaliser, receiving the ball at his feet after a flick-on and fizzing a long range effort just wide.
As the home side pressed, holes were left at the back. Konko and Luis Cavanda both broke clear in the final moments, but last minute blocks ensured the chances came to nothing.
Sampdoria: Romero; Berardi, (De Silvestri 58) Rossini, Gastaldello, Costa; Krsticic, (Soriano 46) Obiang, Munari; Poli; Eder, Icardi (Pozzi 68)
Lazio: Marchetti; Konko, Biava, Dias, Radu; Gonzalez, Hernanes, (Cavanda 82) Ledesma, Mauri, (Ciani 89) Lulic; Klose (Floccari 91)
Goal: Hernanes 31 (L)