LAZIO earned the sweetest of derby victories by effectively ending any hopes Roma had of challenging for the title.
Simone Inzaghi appears to have the Indian sign over the Giallorossi, having recently knocked them out of the Coppa Italia semi-finals.
And this defeat leaves the hosts nine points behind Juventus, with just four games remaining.
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The leaders had drawn 2-2 at Atalanta and a win would have reduced to gap to six points — with the Bianconeri still to come to Roma.
However, they blew the chance when given a slight sniff.
Balde Keita netted an early opener in fourth derby of the season as Lazio after 12 minutes — firing low past Wojciech Szczesny.
The Biancocelesti have performed above expectations this season after a turbulent summer.
Inzaghi stepped in after Marcelo Bielsa’s 48-hour stint as boss and has led the club to a Coppa Italia final and Europa League-qualification via the league.
And they were comfortably the better team in the first 45 minutes.
However, despite their lacklustre showing, Roma were given a lifeline when Kevin Strootman won a controversial penalty.
Captain for the day, Daniele De Rossi, stepped up and kicked the ball into the ground, but was lucky to see his effort bobble into the bottom corner.
But the second half started in the same way as the first and Lazio re-took the lead through a Dusan Basta strike from the edge of the box.
Roma threw on Francesco Totti, but the inspirational 40-year-old icon couldn’t help his side.
Sergej Milinkovic-Savic showed why he is so highly-sought after with a brilliant performance for Lazio.
With any title hopes evaporating, Roma pushed forward — only to be caught out on the break right at the death.
Senad Lulic drove forward and set up Keita, who calmly slotted past Szczesny to cue pandemonium from Inzaghi and his coaching staff.
There was still time for the inevitable red card, as Antonio Rudiger was sent off for a shocking challenge.
Despite insisting before the match it would not be his final derby, this could be a sad way for the legendary Totti to bow out against his fiercest rivals.
But, spare a thought for De Rossi, who is set to finish as a runner-up in Serie A for the EIGHTH time without ever lifting the trophy.