Francesco Totti's stoppage-time penalty clinched Roma a 3-2 victory against Sampdoria after torrential rain had delayed the start of the second half at the Olympic Stadium by an hour.
Veteran striker Totti, a half-time substitute for Diego Perotti, converted his spot-kick into the bottom corner in the third minute of time added on after Milan Skriniar's foul on Edin Dzeko to snatch Roma's second Serie A win of the season.
Former Manchester City striker Dzeko had fired home in the 61st minute to haul his side level after first-half strikes from Sampdoria pair Luis Muriel and Fabio Quagliarella had cancelled out Mohamed Salah's early opener for Roma.
Roma, who failed to reach the Champions League group stages last month after a 4-1 aggregate defeat to Porto, let slip a two-goal lead to draw 2-2 at Cagliari last Sunday and went in at the interval 2-1 down here despite taking an eighth-minute lead through Salah's header.
Colombia international Muriel fired Sampdoria level from a tight angle 10 minutes later and the visitors took the lead four minutes before the break when Quagliarella steered home Ricardo Alvarez's ball in across the face of goal from close range.
The start of the second half was delayed by an hour after heavy rain had left parts of the playing surface under water and flooded the players' tunnel, but the match resumed 10 minutes after a 4.55pm pitch inspection.
Roma got back on level terms in the 61st minute when Totti played in Dzeko in the penalty area and the Bosnia and Herzegovina international buried his finish.
Sampdoria goalkeeper Emiliano Viviano twice denied Salah with fine saves, but Roma were handed one last chance in the dying moments when substitute defender Skriniar impeded Dzeko in the area and Totti held his nerve.