While the hosts lost to Ludogorets in Bulgaria, their visitors were suffering a 2-0 defeat against Real Betis, who are now favourites to top Group C.
Match preview
Having made few changes to his side for last week's Europa League opener, Jose Mourinho was surely expecting a continuation of Roma's continental form from last season, in which they went all the way in the inaugural Europa Conference League and lifted the trophy in Tirana.
However, with their game against Ludogorets still goalless inside the final 20 minutes, the Giallorossi imploded for the second time in a matter of days, having just lost 4-0 to Udinese in Serie A.
The Bulgarian champions scored twice past debutant goalkeeper Mile Svilar in the closing stages, with the second coming only moments after Eldor Shomurodov seemed to have salvaged a point with his 86th-minute strike.
Roma are therefore on the back foot already, and pressure to produce another result to follow Monday's 2-1 win over Empoli is certainly building.
Once again to the fore, following his summer arrival from Juventus in a blaze of publicity, Paulo Dybala not only scored the opening goal in Tuscany but also produced a peach of a delivery for Tammy Abraham to later steer home the winner from close range.
Already a fan favourite at the Olimpico after a few short weeks, Dybala will surely be central to Roma's hopes of progress in the Europa League - as will their form in the Eternal City: the Giallorossi are unbeaten in 19 European home games since February 2019; winning 13 times in the process.
In contrast to their illustrious hosts' home record in Europe, HJK Helsinki travel to Italy having faltered in the Finnish capital just last week, against Real Betis.
Toni Koskela saw his side hold on until first-half stoppage time against one of La Liga's top teams, but Willian Jose's double either side of the break decided the game in the favour of Manuel Pellegrini's men.
HJK took the long route to reach Group C, where they start as outsiders to qualify for the knockout stage as the section's lowest-ranked club: after claiming their 31st domestic title last season, they entered Champions League qualifying in July's first round.
Having edged past Latvia's RFS by way of a penalty shootout, they were ultimately eliminated from Europe's top tournament by Viktoria Plzen, but made it past both Maribor and Silkeborg to claim a share of the group stage riches.
Though HJK did not enjoy the best start to their campaign last week, they have continued to strengthen their position in the Veikkausliiga, and four straight league wins - including against FC Honka on Sunday - saw them finish two points clear at the top ahead of the upcoming playoffs.
After picking up just six points from their six matches in the Conference League last term, even matching that tally this year would represent an achievement, but if they were to take three home from Rome, Koskela and company would be forever preserved as heroes in Helsinki.
Roma Europa League form:
Roma form (all competitions):
HJK Helsinki Europa League form:
HJK Helsinki form (all competitions):
Team News
Set to continue their relentless schedule right up until the international break, Roma will once again refresh their starting XI on Thursday, but a spate of injuries is not aiding Jose Mourinho's cause in that regard.
Wing-backs Rick Karsdorp (knee) and Nicola Zalewski (hip) have both been sidelined of late, joining Marash Kumbulla, Stephan El Shaarawy and long-term absentee Georginio Wijnaldum in the treatment room.
In better news for the hosts, Nicolo Zaniolo is now in contention to feature from the bench, after making his return to the squad in Empoli. Meanwhile, Rui Patricio should again step aside for cup goalkeeper Mile Svilar, and Andrea Belotti may start up front.
HJK still have star striker Roope Riski out of action with a knee injury, so Malik Abubakari - scorer of the decisive goal in their playoff win over Silkeborg - should lead the visitors' attack.
Captain Miro Tenho will helm the back three, which lines up ahead of Northern Ireland international Conor Hazard - the 24-year-old goalkeeper is currently on loan at the club from Celtic.
Roma possible starting lineup:
Svilar; Mancini, Smalling, Ibanez; Celik, Camara, Pellegrini, Cristante, Spinazzola; Dybala, Belotti
HJK Helsinki possible starting lineup:
Hazard; Raitala, Hoskonen, Tenho; Soiri, Lingman, Vaananen, Tanaka, Browne; Hostikka, Abubakari