Gianluca Mancini gave Roma a slender advantage in their Europa League quarterfinal with AC Milan after netting the only goal in Thursday's 1-0 win at the San Siro.
Just as in the weekend's Rome derby in Serie A, Mancini headed home the winner from a Paulo Dybala corner to earn Roma a precious victory against their fellow Italians.
Mancini has had an eventful few days as he was fined 5 000 euros ($5 427) on Tuesday for waving a flag depicting Lazio supporters as rats in his post-derby celebrations.
The 27-year-old's sixth goal of the season, in the 17th minute, gave his team a hard-fought victory and a lead to defend at next week's second leg in Rome, when Roma will continue their bid for a third European final in as many years.
"I'm so happy. I've been spoken about a lot in the last few days but to win the derby and come here and win in the way we did, like a proper team, is a huge joy," said Mancini to public broadcaster Rai.
"It's a great night for us. I couldn't have asked for more from this week."
Thursday's win also continued former Italy midfielder Daniele De Rossi's remarkable start as coach of his boyhood club who beat Milan at the San Siro for the first time since October 2017.
De Rossi has completely revitalised Roma since taking over from Jose Mourinho, who was dismissed in January after a league thumping at the hands of Milan.
Roma have only lost twice under his charge, to Italian champions-elect Inter Milan and Brighton in the previous round of the Europa League when that last-16 tie was decided in the first leg.
Milan, who struck the woodwork late on through Oliver Giroud, now face an uphill task to get something from their season as they trail Inter by 14 points in Serie A.
- Mancini on target -
Stefano Pioli's side, who came into Thursday's clash on a run of seven straight wins, could even concede the league title to their local rivals in the next derby with Inter on Monday week, making next week's return a huge fixture for the seven-time European champions.
"I think we can play much better than this and we have the chance to do so, because we are a better team than we showed tonight," said Pioli to reporters.
Under De Rossi Roma have become a more fluid team than they were under Jose Mourinho and they were deservedly in the lead when Mancini headed in the opener from his team's first real chance of the game.
Mancini's goal came immediately after Mike Maignan pulled off a super stop to deny Stephan El Shaarawy's deflected shot and it prompted an immediate reply from Milan.
Romelu Lukaku twice cleared off the line as the hosts caused panic with three consecutive corners before piling on the pressure in search of a leveller.
Tijjani Reijnders had a good low effort pushed away three minutes before the break but Milan struggled to break down a well organised away team.
After the break a similar pattern emerged as Roma deftly held off the frustrated hosts before trying to pounce on the break, with Lorenzo Pellegrini and Bryan Cristante both dragging efforts wide.
Milan continued to push but kept bumping up against a Roma rearguard action which would have made Mourinho proud, with Mile Svilar tipping over Yacine Adli's mishit cross with 15 minutes to go.
And Giroud wasted a golden chance to level the tie with three minutes remaining when he hit the crossbar from close range after being perfectly set up by Samuel Chukwueze.