The evergreen Totti - 38 and still going strong - bundled a Jose Holebas cross into the back of the net for his and Roma’s second as they fought back from 2-0 down at half time.
Totti, now in his 23rd season with the Rome outfit, had earlier pulled a goal back to give Rudi Garcia’s side a glimmer of hope.
After scoring, ‘Il Gladiatore’ hurdled the advertising hoardings and took a mobile phone from a Roma official, stopping to take a selfie of himself with the fans in the Curva Sud stand behind him.
He told TV reporters at the match: “I thought about it during the week. Although it’s in fashion, I don’t usually take them because I want my private life to stay that way, but this was a special occasion, something to be remembered for a long time.”
The former Italy striker, who was awarded the Order of Merit of the Italian Republic, has an intriguing history of vital goals against Lazio.
In 1999, he scored during the final minutes of the second ‘Derby della Capitale’ of the season, lifting his top to show a t-shirt with the message ‘Vi ho purgato ancora’ (I’ve purged you guys again), a reference to the previous derby clash, when Totti had helped Roma to a 3-3 draw after being 3-1 down.
During another derby, he scored a goal and grabbed a sideline camera, pointing it towards the Roma supporters.
Sunday’s match was Totti’s 40th Derby della Capitale appearance, and his brace took him to 11 goals in the fixture, equalling Roma legend Dino Da Costa’s record set during the 1950s.
Totti, who made his debut in 1994 aged 17 - added: “For a Roma player, that’s the most wonderful thing that can happen.
“It wasn’t easy to turn this result around, but we were moreclinical and proved we can fight for the Scudetto.”
Rudi Garcia paid tribute to the legendary forward, describing him as a ‘genius’, adding: “He said before the match that this would be his game and he was right.”