Menez had the first chance when chesting down an acrobatic Francesco Totti flick, forcing a save out of Marco Storari at the near post. From the resulting corner Juan's audacious overhead kick was just wide from six yards.
Mirko Vucinic skipped past two tackles down the left, but the pull-back was just too long for Totti. The move continued and Simone Perrotta's volley was well smothered by Storari.
Roma did break through after 14 minutes with their captain. Totti started and finished the move, combining with Vucinic down the left and carrying on into the box where he was able to side-foot home from eight yards. It was his first goal since January.
Vucinic ran on to a through ball and flashed the angled drive across the face of goal. Storari seemed to get a hand to it, but the corner was not given.
Del Neri introduced both Fernando Tissone and Daniele Mannini for the second half. Tissone blasted over from distance, but it was Pazzini who got the goal for Sampdoria.
A chipped Cassano cross from the left found Pazzini relatively unmarked at the back post to nod in, as John Arne Riise left him with far too much space and the header down went between Julio Sergio's legs.
Toni replaced Perrotta for the trident attack and nearly scored with his first touch! He got on the end of a Pizarro free kick at the back post and his header was well parried from point-blank range.
However, Sampdoria struck on the counter-attack with Pazzini's second of the game. Daniele Mannini got down the left and rolled his cross low for Pazzini to tap in from close range, having got away from Riise.
(GSM) - Claudio Ranieri was shocked after Roma's title chances were seriously dented by Sampdoria. After the match, the tactician said they "must carry on as if nothing has happened."
The Giallorossi lost the leadership after home defeat (1-2) and now trail Internazionale by two points.
“If we had drawn this match then it would’ve been the same thing. We were in charge of our own destiny and now we aren’t,” confessed Ranieri.
“We must carry on as if nothing has happened. We had probably our best first half performance since I’ve been here.
“Unfortunately we did not remain as solid after the break and Samp took advantage. I tried to create a few more crosses for Luca Toni, but we couldn’t find the goal.”
The run-in now sees Inter face Lazio at the Olimpico, Chievo at San Siro and finally practically relegated Siena away from home.
Roma travel to Parma, welcome Cagliari and end the season at the Bentegodi with Chievo.
“I don’t know where Inter are likely to drop points. All I know is that we must give our all. The sad fact is our fate is no longer in our hands,” added Ranieri.
“The Scudetto will be decided in the final round. We have fallen and must get back on our feet. Luck was on our side in the derby, but not tonight.
“We certainly need to end the season well. Inter are strong, so compliments go to them and to Roma for an impressive campaign.”
ROME (AFP) - Giampaolo Pazzini scored a brace as Sampdoria stunned AS Roma 2-1 to deal a potentially fatal blow to the capital-based club's title hopes.
Samp came from behind after a torrid first half to score the shock win that sees Roma drop to second in Serie A, two points behind champions Inter Milan, who beat Atalanta 3-1 on Saturday.
Not only did the Genoa-based club end Roma's 24-match unbeaten run in the league but they also kept themselves in fourth and the crucial final Champions League qualification position, two points ahead of Palermo, who beat AC Milan 3-1 on Saturday.
Roma coach Claudio Ranieri said: "We have to keep going as if nothing has happened, we played the best first half of my time here."
"We have to concentrate on ourselves, the title will be decided at the end in Verona (where Roma play their final game). We've fallen over and we need to get up.
"We're here because (Inter) dropped points along the way. They're very good, well done to them but also to us."
Roma's first half performance was worthy of champions as time and again they carved Sampdoria open but the only surprise was that they managed just one meagre goal from their domination.
The hosts were in blistering form from the off and French winger Jeremy Menez brought a save out of Marco Storari before Brazilian centre-half Juan sent an overhead bicycle kick from a corner just wide.
After Storari had saved from Simone Perrotta, captain Francesco Totti gave Roma a 14th-minute lead.
Mirko Vucinic picked up the ball on the left and centred for Totti to glance a shot into the far corner.
And just five minutes later it was almost two as Vucinic released Totti in the inside left channel but his shot hit the near post.
Storari saved again from Menez while Totti and Vucinic were both off target as Roma kept the pressure on until half-time.
But despite the one-way traffic of the first period, Sampdoria equalised soon after the restart as former Roma forward Antonio Cassano made space on the left and crossed to the back post where Pazzini's header found a gap between goalkeeper Julio Sergio's legs.
Roma were quickly back on the attack as Juan headed over from a corner but Sampdoria remained resolute.
Midway through the half coach Claudio Ranieri sent on striker Luca Toni as a last desperate throw of the dice.
Toni soon had an identical chance to Pazzini but this time Storari saved with his legs, before the on-loan Bayern Munich man had a strike ruled out for offside.
And nine minutes from time Storari tipped over a rocket from John-Arne Riise.
But four minutes later Roma were hit with a sucker punch as Sampdoria countered and Daniele Manini crossed for Pazzini to sidefoot home his second.
Earlier Juventus kept alive their hopes of Europa League football next season with a routine 3-0 win at home to Bari.
Vincenzo Iaquinta scored a brace in the second period, sandwiching an Alessandro Del Piero penalty.
They are sixth and six points clear of eight-placed Genoa with three to play, meaning they are virtually assured of European football next season.
Livorno became the first club to be relegated this season despite a 3-1 win at home to Catania as Bologna's 2-1 home success against Parma left Livorno 10 points from safety with just three to play.
Siena are all but mathematically down after their 4-1 defeat at Udinese.