The Uruguayan midfielder added to his goal in last weekend's North London derby triumph with this crucial match-winner as Huddersfield's brave resolve was broken late on.
With the three points, Arsenal climb above Tottenham Hotspur and Chelsea into third in the Premier League table and extend their unbeaten run in all competitions to 21 matches.
It took a while for the game to come to life, starting when Arsenal squandered a couple of golden opportunities just prior to the half-hour mark. The first fell to top scorer Pierre-Emerick Aubameyang who could not divert Granit Xhaka's errant shot on target from eight yards out.
His strike partner Alexandre Lacazette was even more wasteful moments later when he was found unmarked on the penalty spot, only to lose his footing while pulling the trigger, sending his shot high over the crossbar.
Referee Paul Tierney showed seven yellow cards in the space of 24 minutes before the break, two of them for simulation against Arsenal's Xhaka and Shkodran Mustafi, but the score remained goalless thanks in part to a controversial offside call.
While Lacazette was offside from Aubameyang's initial flick-on, a short back-pass from Mathias Jorgensen appeared to bring the Frenchman back into play, and he rounded Jonas Lossl and slotted home only for the flag to go up.
Lossl was another reason that the deadlock remained intact at half time, producing a fingertip save to deny Torreira whose 25-yard piledriver was heading into the top corner.
Unai Emery introduced Alex Iwobi and Henrikh Mkhitaryan at the interval but neither could provide the creative spark to get the supply line to Aubameyang going. The Gabonese was living off scraps and when a half-chance did come his way on 64 minutes, he could not react quickly enough at the back post to direct his header on goal.
Aubameyang ended up being the supplier himself for the Torreira goal on 83 minutes, having failed to bring Matteo Guendouzi's dink under control the striker lifted a cross into the centre for his teammate to acrobatically volley home from close range.
Guendouzi became the third Gunner to be punished for diving, and referee Tierney was not fooled by Laurent Depoitre's theatrics in the box either as the Terriers striker tried to buy the visitors an equalising chance from the spot.
Huddersfield's third defeat in the space of a week sees them drop into the relegation zone, but it was a spirited display against an Arsenal team who again turned half-time parity into three full-time points.
ARSENAL (3-5-2): Leno; Bellerin, Lichtsteiner (Iwobi 46'), Mustafi (Monreal 66'), Sokratis, Kolasinac; Guendouzi, Torreira, Xhaka; Aubameyang, Lacazette (Mkhitaryan 46')
HUDDERSFIELD (4-4-1-1): Lossl; Smith (Hadergjonaj 60'), Kongolo, Schindler, Jorgensen, Lowe; Hogg (Bacuna 52'), Mooy, Williams (Durm 70'); Pritchard; Depoitre body check tags ::