Luis Suarez's close-range header had sent the visitors ahead in the 21st minute, but a long-range strike from Florenzi ensured that the Italian side gained a share of the spoils.
In Group E's other fixture, Bayer Leverkusen recorded a 4-1 home win over BATE Borisov.
Here, Sports Mole dissects the 90 minutes of action in Rome.
On target: 3
On target: 6
Was the result fair?
For the neutral, this was a great match, with the fixture providing end-to-end football and a fascinating tactical battle, especially in the second period. For all of the positives, however, clear chances were very much at a premium. As expected, it was a tight opening 20 minutes in Rome and Barcelona took the lead with the first real chance of the match when Suarez headed an Ivan Rakitic cross into the back of the net from close range. It did appear that the Catalan side would go on to win it quite comfortably, but one of the all-time great Champions League goals levelled the scores in Rome.
Not too much was on for Florenzi when he burst past the halfway line, but a stunning 60-yard effort found its way into the back of the net. Barcelona remained the team in control of the possession, as the statistics demonstrate, but the majority of the Spanish side's efforts were from half-chances or strikes from distance. Lionel Messi and Jordi Alba both came close to winning it for Barcelona late on, but it would have been a little harsh on Roma, who defended well all night. If one team deserved to win it, it would have been the visitors, but Roma were well worth a point in the end.
It was always going to be a tough ask for Roma to record all three points against this Barcelona machine, but head coach Rudi Garcia can be proud of his team's performance in Rome. As touched upon, it was a fairly tight start to the match, but Mohamed Salah and Edin Dzeko both showed signs that they would trouble Barcelona as matters developed. Roma were unhappy with the awarding of the Barcelona opener, feeling that Messi had fouled Lucas Digne in the build-up, but it would have been a harsh decision to disallow the goal. The hosts were then a touch fortunate not to concede a penalty in the 25th minute when Suarez went down under contact from Wojciech Szczesny, only for the referee to shake his head. Roma were not really in the game as the 30-minute mark approached, but they levelled the scores in stunning style.
Florenzi seemed almost in tears when he realised that he had found the back of the net from such an incredible distance and the equaliser inspired Roma in the latter stages of the first period, with Dzeko's physicality and Salah's pace causing problems. Daniele De Rossi and Radja Nainggolan were also excellent in the middle of the park, which continued throughout the second period. Messi remained the biggest threat for Barcelona, but clear chances after the break were very much at a premium. Enforced changes meant that the tempo was slow for long spells of the second half, but Roma continued to defend impressively on what was a frustrating night for the European champions. Neymar and Messi both had chances to win it late on, but Roma had that little bit of luck needed to stop the Catalan outfit from winning. There is no question that Garcia had a gameplan to stifle Barcelona after the break and it worked a treat.
There was only really one surprise in the XI that Luis Enrique selected, with Jeremy Mathieu called into the team at the expense of Javier Mascherano. In the end, it proved to be a good call from the Barcelona boss, with Dzeko's aerial threat proving a problem, especially in the first period. When Barcelona took the lead through Suarez, who could not miss with a close-range header, it did seem that all the points would be heading back to Camp Nou. A failed penalty shout seemed to disrupt their tempo, however, in addition to conceding a spectacular long-range effort. Marc-Andre ter Stegen's position might well be looked at, but the goalkeeper was not even that far off his line, which makes the goal even more impressive. Even at 1-1, Barcelona still looked in control of proceedings and indeed that continued early into the second period, with Messi and Neymar both coming close in an incident that forced Roma to change their goalkeeper.
A host of changes and fouls harmed the tempo for the 25-minute period that followed, however, with neither team really threatening to score a second goal. Barcelona, as mentioned, had a couple of opportunities around the 80-minute mark, but neither Messi nor Neymar could find the back of the net, before Alba was denied late on. Messi was once again in fine form for the Catalan side, but it was a fairly quiet night for Suarez - despite his goal - and Neymar, who only really showed his excellence in flashes. Defensively, the visitors were not really concerned for long spells, but their lack of variation in the final third would have been frustrating for the supporters. It is a game that Barcelona will feel that they should have won, but a point away to their biggest challengers in Group E is far from a bad result.
Sports Mole's man of the match
Daniele De Rossi: The legs might not move as quickly as they once did, but the 32-year-old's football brain remains in full working order. It was a real captain's performance from the Roma midfielder, who got about the pitch very well indeed and made challenge after challenge in key areas. He was not really involved in an attacking sense, but the protection that he offered to the home side's defence was absolutely key.
Nainggolan had a strong game for Roma, but he was guilty of a really poor challenge in the second period. Barcelona's Rafinha had barely been on the field 90 seconds when the Belgian international lunged in and it forced the visitors to replace the Brazilian, just four minutes after entering the field. Nainggolan was yellow-carded for the poor tackle.
Barcelona will feel that they should have been awarded a first-half penalty when Szczesny challenged Suarez inside the box, but Dutch official Bjorn Kuipers was not interested. Aside from that incident, the 42-year-old actually had a fairly quiet night - issuing just two yellow cards. The official also allowed the game to flow in the correct areas.
Roma: The Italian side return to Serie A action at home to Sassuolo on Sunday afternoon. Their next Champions League group match is away to BATE Borisov on September 29.
Barcelona: Enrique's side will attempt to make it four straight wins at the start of the new La Liga season when they host Levante on Sunday. They also return to Champions League duty on September 29, at home to Bayer Leverkusen.