Roma's players and fans will go against everything they hold sacred this weekend when they cheer on bitter rivals Lazio against Inter.
Claudio Ranieri's Roma surrendered the Serie A lead to reigning champions Inter last weekend when they lost for the first time in 25 league matches at home to Sampdoria.
Now with three games left, they must first win at Parma on Saturday before risking the wrath of the Roman gods by supporting Lazio for the first time in their lives in the home match with Inter on Sunday night.
Roma and Lazio have one of the most heated rivalries in football with the former's win in the city derby earlier this month prompting an on-pitch brawl and violence on the streets.
Some Lazio fans are so desperate for Roma to miss out on the title that they have besieged internet message boards to demand their side lose on Sunday now they are almost safe from relegation, six points above the drop zone.
However, coach Edy Reja, banned from the dugout for arguing with officials in last Sunday's win at Genoa, is having none of it.
"Safety has still not been reached and against Inter we cannot afford any slips. We will try to get the best result possible," he said.
Inter, two points ahead of Roma as they seek a fifth straight Scudetto, meet Lazio on a high after reaching the UEFA Champions League final having overcome Barcelona on Wednesday.
The Lazio clash looks to be Inter's most difficult on paper in the title run-in and Jose Mourinho's men lost on their previous visit to Rome's intimidating Stadio Olimpico, succumbing to Roma last month.
Roma will not have it their own way either against mid-table Parma and their former Inter striker Hernan Crespo.
"We've got to believe, the battle for the Scudetto is not over," Ranieri said.
Treble-chasing Inter will be back in the capital again next Wednesday for the Coppa Italia final against who else but Roma.
Faltering AC Milan, in third, need a win at home to Fiorentina on Saturday with Sampdoria four points behind them in the race for the last automatic Champions League berth.
Samp, two above Palermo in the fight for fourth spot and a Champions League qualifying round place, host already-relegated Livorno on Sunday.
Siena will follow Tuscan neighbours Livorno through the trapdoor if they fail to beat Palermo or Bologna pick up at least a point at third-bottom Atalanta, who could also go down if they lose and other results go against them.