The capital outfit had seen Inter drop points away to SPAL in the day's earlier kickoff but could not take advantage as Duvan Zapata scored the only goal of the game after Alessandro Florenzi had missed a penalty for the hosts.
Roma are now winless in their last seven matches across all competitions, while sixth-placed Sampdoria close the gap on their opponents down to four points courtesy of only their third away league win of the season.
The visitors had the first chance to break the deadlock after only nine minutes when Gianluca Caprari found space on the edge of the area, only to fire his subsequent effort narrowly wide of the target.
Sampdoria continued to look the most likely to open the scoring, though, and Edgar Barreto was the next to come close when he drew the first meaningful save from Roma keeper Alisson Becker with a 20-yard strike.
The busy Alisson needed to be alert again shortly before the half-hour mark when he reacted quickly to turn Zapata's effort wide of the post after the Sampdoria man had broken into the box.
Roma did have the ball in the back of the net just five minutes after that, but Kostas Manolas's effort was ruled out for offside as the celebrations were cut short.
The hosts had an even better chance to take the lead with just six minutes remaining of the first half when Bartosz Bereszynski was penalised for a handball inside the area, only for Florenzi to see his subsequent spot kick kept out by Emiliano Viviano.
The two sides went into half time still goalless, but Roma were quickly on the front foot upon the restart and squandered another glorious chance to break the deadlock when Cengiz Under was thwarted by Viviano from point-blank range five minutes into the second half.
Indeed, it was the Sampdoria shot-stopper who was keeping the visitors in the game, and he was called into action again shortly afterwards to make another close-range save, this time to deny Lorenzo Pellegrini from inside the six-yard box.
The flow of chances eventually dried up for the home side, and they were punished for their profligacy 10 minutes from time when Zapata applied the finishing touch to a Nicola Murru cross for the only goal of the game.
Roma could not muster a response in the closing stages as Sampdoria held out for their first away win since November 4, ending a five-match winless run on the road.
The hosts, meanwhile, are now winless in their last four home outings and have taken just two points from the last 18 on offer in Serie A as their top-four hopes suffer another blow.
ROMA (4-3-3): Alisson; Florenzi, Manolas, Jesus, Kolarov; Pellegrini (Defrel, 70'), Strootman, Nainggolan; Under (Perotti, 72'), Dzeko, El Shaarawy (Antonucci, 78')
SAMPDORIA (4-3-1-2): Viviano; Bereszynski, Silvestre, Ferrari, Murru; Barreto, Torreira (Capezzi, 86'), Linetty; Ramirez (Alvarez, 72'); Zapata, Caprari (Kownacki, 62')