The Argentine took less than half an hour to open his Blucerchiati account for the second time, after arriving on loan from Catania on transfer deadline day. Genoa's seven match unbeaten record at the Marassi comes to an end.
The Grifone had eased to a 3-0 victory back in Week 3, but Samp ensured there would be no repeat of that scoreline. This match was originally due to be played Sunday lunchtime, but a debate between local MPs and fans from both sides saw the game pushed back.
Genoa were unchanged from last weekend's 3-3 draw at Fiorentina. Pedro Obiang made way for Lopez in the Sampdoria lineup, while Vasco Regini returned from suspension to start ahead of Andrea Costa in defence.
Both sides set their stalls out to attack. Matuzalem broke quickly and flashed a dangerous ball across the six yard box, which was inches ahead of Alberto Gilardino. At the other end, Angelo Palombo sent a free kick into the side netting and Mattia Perin clawed away a Lorenzo De Silvestri cross before Lopez could pounce.
Samp opened the scoring on 24 minutes. Lopez played a give and go with Eder, whose eloquent first touch lofted the ball perfectly into the Argentine's path for him to squeeze a shot past Perin at the far post.
Gilardino was denied a penalty after tangling with Daniele Gastaldello in the box and Lopez was denied a second goal, hitting his low shot straight at Perin.
Genoa went to sleep defending a free kick on 38 minutes. Manolo Gabbiadini lofted the ball into the box and caught Perin by surprise, with the ball bouncing off his chest and into his arms. Shkodran Mustafi made an attempt to slide in, but the ball was too far ahead of him.
The home side woke up in the closing stages of the first half. Gilardino headed a Moussa Konate cross straight at Da Costa, who then flew to tip Andrea Bertolacci's swirling shot over the bar. Lopez was let off for an accidental handball in the box after a corner bounced off his foot and onto his hand. Luca Antonelli did put the ball in the net on 41 minutes, but play was rightly called back for offside. Antonelli then scuffed another effort wide of the post.
After the restart, Perin kept Sampdoria at bay with a couple of comfortable saves and Matuzalem curled a tame free kick into Da Costa's gloves.
Genoa had a second goal chalked off on 65 minutes. Konate finished a flowing passing move, but was a yard offside. The frontman made way for the returning Giuseppe Sculli, with the on loan attacker making his second bow for the Grifone.
From a corner, Genoa players got in the way of each other during a goalmouth scramble, Bertolacci's point blank header was too high and Sculli couldn't direct his own header towards goal.
Genoa's frustration accumulated a couple of bookings, but Samp couldn't capitalise from the resulting set pieces. Gabbiadini sent a disappointing free kick into the stands, before Alessio Sestu wasted a glorious chance to put the game to bed five minutes from time. The substitute made a hash out of connecting with Gabbiadini's delivery from six yards and really should have marked his debut with a goal.
The home side kept pushing. During a frenetic finish, Gastaldello chested a Gilardino effort off the line. Ioannis Fetfatzidis pumped another ball into the danger area, but the lack of a crucial touch from a Genoa player proved telling once again, as Da Costa smothered the ball.
Genoa: Perin, Antonini, De Maio, (Fetfatzidis 48) Burdisso; Antonelli, Marchese, (Calaio 83) Matuzalem, De Ceglie; Konate, (Sculli 66) Bertolacci, Gilardino
Sampdoria: Da Costa, De Silvestri, Mustafi, Gastaldello, Regini; Palombo, Krsticic; (Renan 89) Gabbiadini, Soriano, (Obiang 72) Eder; (Sestu 78) Maxi Lopez
Goals: Maxi Lopez 24 (S)