Pjanic was booked just before half timeand received a second yellow card for handball in the 72nd-minute as Roma's five-match winning run in the league came to an end.
Chelsea's defeat to West Ham earlier in the afternoon had given Liverpool the chance to leapfrog them and while Manchester City ended the day top of the Premier League, this felt like a huge three points for Jurgen Klopp's side as they came
Even the second-half introduction of Alexis Sanchez - featuring for the first time since suffering a hamstring injury in November - could not spark Arsenal, who lost at home in the league for the first time since the opening weekend of the season
"Go easy on me, baby / I was still a child / Didn't get the chance to / Feel the world around me / I had no time to choose / What I chose to do," she sings before the video turns to color. Watch below.
Messi and his forward colleagues Neymar and Luis Suarez headed to Emirates Stadium with 91 goals between them this season, but were initially starved of opportunities by an Arsenal side playing with impressive discipline and intensity.
Ronaldo had a chance to win the game after Chiesa was fouled but Pierluigi Gollini guessed right to save his kick. Former Aston Villa keeper Gollini had an excellent game and denied Alvaro Morata with a good save.
Captain Martin Odegaard added the second deep into stoppage time at the end of the game, turning in from a tight angle after his initial cross had been blocked.
And it was day of joy for striker Richarlison, who has struggled to find consistency and momentum in his Spurs career but was the spearhead here with a goal either side of half-time as Newcastle wilted in the face of some scintillating attacking
And their woeful night was nearly made worse when Declan Rice gave away a penalty in the final minute of injury time, but Said Benrahma's effort was saved by David Raya.
The five-time winners continued to push forward and were rewarded as Mohamed Salah's strike looped in via a huge deflection off Simon Kjaer, but then Firmino, presented with the chance to give the home side breathing space, struck a penalty
Chelsea had the better of the second half but could not carve out the chance to score a potentially vital second. Manager Tuchel will still be very satisfied with both the performance and result.
The wave of attacks from the Reds was unrelenting and Cody Gakpo had a goal disallowed for Nunez's foul on Charlie Taylor, while Salah rattled the crossbar - all before half-time.