The Finn netted the opening goal with a clinical header from a corner just past the hour mark before Pacheco sealed their progress two minutes from time.
It was a particularly sweet moment for Dalla Valle following his goalscoring heroics in last week's Liverpool Senior Cup semi-final victory over Tranmere Rovers.
Overall it was a hard-fought triumph for John McMahon's side, with skipper Jay Spearing a calming influence in midfield.
It means the Reds' hopes of a possible treble remain in sight, with the league title run-in and two cup finals to look forward to.
Despite a host of fixture postponements, McMahon's men have continued their fine form, winning 12 of their 13 matches since the opening day defeat at Blackburn Rovers.
Going into the clash McMahon was without the injured Chris Mavinga so Steven Irwin took over at left-back while Spearing and Damien Plessis linked up in central midfield.
Wigan also fielded a team with several experienced players and they made a bright start to the game.
Left-winger Rachid Bouaouzan in particular caused Emmanuel Mendy endless problems with his trickery, until the Senegalese defender was forced to leave the field with an injury in the 34th minute.
Liverpool's best chances in the first half fell to Dalla Valle and Pachecho with the Spaniard missing two clear-cut opportunities.
After nine minutes Pacheco's superb pass gave Dalla Valle a chance. The Finn showed great strength to hold off the experienced Steve Gohouri but was denied by a superb stop from Serbian stopper Vladimir Stojkovic.
The game was developing into a physical battle with Dalla Valle and David Amoo in particular on the end of strong tackles.
For their part, Wigan were always dangerous going forward with the classy Joe Holt and Polish schemer Tomasz Cywka causing the Reds problems.
Cywka had two great openings - the best of them came from a sloppy Pacheco back pass that cut his defence wide open
A misplaced pass then gave Pacheco space just outside the box but the Spaniard could only drag the effort wide of goal.
McMahon's side had a golden opportunity to break the deadlock on the stroke of half-time when Irwin's brilliant cross from the right caused all sorts of problems. The ball fell to Pacheco who had a clear sight of goal but unfortunately he fired wide.
Liverpool stepped it up after the break and took their goals brilliantly. The hosts did have their moments but the Reds held firm at the back with Daniel Ayala and Victor Palsson outstanding.
Wigan Athletic: Vladimir Stojkovic, Daniel Redmond, Jordan Mustoe, Antonio Amaya, Steve Gohouri, Jon Routledge, Tomasz Cywka, Joe Holt, Tomasz Kupisz, Callum McManaman, Rachid Bouaouzan.
Liverpool Reserves: Peter Gulacsi, Emmanuel Mendy (Jordy Brouwer 34), Steven Irwin, Daniel Ayala, Victor Palsson, Jay Spearing (Captain) (Nikolaj Kohlert 90), Daniel Pacheco, David Amoo, Lauri Dalla Valle (Nikola Saric 83), Damien Plessis, Alex Kacaniklic. Subs not used: Martin Hansen, Francisco Duran.
Referee: R Metcalfe
Liverpoolfc.tv Man of the Match: Daniel Ayala. A commanding presence at the back and won every header. Victor Palsson also played well at the back alongside Ayala and deserves a mention.