Rudi Garcia's side spurned a number of chances before two second-half goals and a red card for Seydou Keita compounded a miserable match
After spurning a number of chances in the first hour, Rudi Garcia's side were undone by goals from Lorenzo De Silvestri and Luis Muriel as their faltering Serie A form continued.
A late red card for Seydou Keita compounded the misery of the home side, who now find themselves looking over their shoulders at bitter rivals Lazio, who have closed to within a point.
Francesco Totti was recalled to the starting XI after missing the Europa League draw with Fiorentina due to injury, while Radja Nainggolan was forced to sit out through suspension. Sampdoria, meanwhile, replaced Afriyie Acquah with Roberto Soriano and Muriel with Stefano Okaka.
Roma began to dictate proceedings from the off but it took 18 minutes to carve out the first clear chance, as Keita acrobatically volleyed in Alessandro Florenzi's free kick, but the offside flag had been correctly raised.
Minutes later, Gervinho darted forward through the defence and found Juan Iturbe, who in turn played in Totti to the left of the penalty area, but the veteran's shot was straight at Emiliano Viviano.
Totti then spurned another good chance when he failed to get a meaningful connection to Vasilis Torosidis' cross.
Roma continued to do all the pressing and Miralem Pjanic was amazed he could not do better as he slid in with defender Vasco Regini to meet Gervinho's left-foot cross but could only bundle the ball into Viviano's grasp.
The Ivorian, whose pace was a real threat throughout the first half, raced clear of the defence again in the dying minutes but could only prod straight at the keeper.
Roma came flying back out after the break and Totti again fluffled his lines when the goal was at his mercy, contriving to thigh the ball wide of the far post from Florenzi's free kick. Pjanic and Gervinho then got in each other's way in the area following Totti's flick on.
Sampdoria, who had barely threatened for the opening hour, then duly delivered the sucker-punch. Samuel Eto'o skipped his way into the area and De Silvestri prodded home to silence the Olimpico.
The goal saw Roma lose their rhythm and the attack began to look far less threatening. Substitue Daniele Verde's shot over the bar from distance was the best they could muster for some time.
And 12 minutes from time, Samp doubled their advantage. Muriel's brilliant burst forward saw him hit the post with a shot and, after Duncan and Eder kept the ball alive, the Colombian had an even easier finish at the near post.
The whistles began to rain down from the stands as Roma continued to press with little end product until Pjanic drew a good save from the excellent Viviano. But the hosts' misery was compounded when Keita was issued a quick-fire second yellow card after applauding the referee for issuing the first.