Olof Mellberg and Pavel Nedved added the third and fourth goals after injury-and-suspension ravaged Roma ran out of steam.
The win puts second-placed Juve four points behind leaders Inter Milan, who have 10 games remaining and host bottom side Reggina on Sunday.
"We must think about our results without looking too much at Inter," Iaquinta told Sky television.
"We have nine games left and we have to go on the field with the mentality to win all nine."
But Iaquinta, who hopes to be named on Sunday in Italy's squad for the World Cup qualifiers with Montenegro and Ireland, soon had Juve back in the lead.
Zdenek Grygera's cross deflected up off John Arne Riise and former Udinese striker Iaquinta jumped highest to head home.
Riise then cleared Alessandro Del Piero's shot off the line but Juve were not to be denied and Mellberg powerfully headed in a corner before substitute Nedved matched last weekend's scoreline against Bologna with a fierce shot from distance.
Eighth-placed Lazio's hopes of European qualification took another blow in the early kickoff when Delio Rossi's side lost 1-0 at Catania.
Lazio, beaten 3-0 at home by struggling Chievo last weekend, should have equalised but Albano Bizzarri saved Goran Pandev's second-half penalty after the Macedonian had been fouled.
