Belgium midfielder Nainggolan tapped in Miralem Pjanic's pin-point cross eight minutes before the break to secure the victory that puts Roma on 57 points from 24 games.
Juve play their 25th league game of the campaign at home to Torino in the Turin derby on Sunday (1730 GMT).
"We've put a bit of pressure on them, but Juve are a great team," said defender Mehdi Benatia.
"We need to do our jobs and win each match. If we do in the second half of the season what we did in the first we'll be close."
Rudi Garcia's Roma are seven points ahead of third-placed Napoli after a solid display against a committed but uninspired Bologna, who could have equalised in added time if Lazaros Christodoulopoulos had not flashed a close-range header wide.
Rafael Benitez's Napoli take on Genoa on Monday (2000 GMT) after fourth-placed Fiorentina, who have 44 points and are also battling for a Champions League qualifying spot, travel to in-form Parma who are sixth (1800 GMT) with 36 points.
Roma have only let in 11 goals in the league so far this season, with 16 clean sheets in their 24 matches, and looked solid despite having to play with Taddei and Alessio Romagnoli in the absence of three injured fullbacks.
"We had a lot of players missing but we're a good group. Every time the manager calls on someone they respond well," added Benatia.
DEADLOCK BROKEN
Bologna have been harder to beat since Davide Ballardini took over as coach in early January but they remain 16th on 21 points, two points above the relegation zone, having won only twice since the end of October.
Roma had already hit the post through in-form striker Mattia Destro but created little else when 25-year-old Nainggolan broke the deadlock.
Gervinho sucked in Bologna's defence with a characteristic burst from midfield before laying off to Pjanic, who spotted the Belgian racing unmarked into the area and clipped a perfect inswinging cross for an easy finish.
The home side were more aggressive in the second half, but Roma were dangerous on the break and it was only poor final passes that stopped the away side from adding to their lead.
Taddei thumped their clearest chance straight at Bologna keeper Gianluca Curci with 15 minutes left, and it almost proved costly.
After a dreadful pass from substitute Michel Bastos ended a counter-attack in which Roma had two men racing towards goal completely unmarked, Christodoulopoulos flew at Davide Moscardelli's cross only to glance what looked to be a certain equaliser wide to the relief of the several thousand away fans.
"It's a huge win. In the second half we had lots of counter-attacks and chances to score the second goal. We suffered a lot, in particular at the end of the game," said Garcia.
"We are playing for something really special and the players need to understand that."
(Reporting by Terry Daley; Editing by Ken Ferris)
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