The Australian forward missed a glorious chance after 15 minutes but produced an excellent diving header to convert Robert Koren's cross shortly after.
On-loan Arsenal goalkeeper Vito Mannone made his debut for Hull but Preston gave him little to think about in the opening period aside from an early Adam Barton effort.
After the interval North End posed a greater threat and Iain Hume's 25 yard drive was excellently tipped onto the inside of the post by Mannone.
But a horrible error from Sean St Ledger - playing out position at left-back after North End skipper Callum Davidson departed at half-time - allowed Garcia to set up Nicky Barmby for his third goal of the season.
Jay Simpson could have added further gloss to the scoreline for Hull when he hit the post in stoppage time, but it did not matter as a beleaguered North End were left rooted in the relegation zone.
North End boss Darren Ferguson made three changes to the side that suffered a 2-1 defeat to Barnsley with Billy Jones, Paul Coutts and Keith Treacy making way for Barton, Wayne Brown and Iain Hume.
Hull made two changes from the midweek draw at Leeds, as Mannone ousted Matt Duke in goal and Koren returned from a hamstring injury to replace the suspended John Bostock.
Mannone sprung into action in the sixth minute, beating away a rasping 20 yard drive from Barton. Jon Parkin poked home the rebound from an offside position.
Garcia shot wastefully wide in the 15th minute after Koren's measured pass caught out the Preston defence, but the same combination gave Hull the lead moments later.
Koren was the architect, marauding down the right to deliver a delicious cross which Garcia finished superbly with a full-length diving header.
The Slovenian playmaker should have doubled Hull's advantage when Anthony Gerrard's pass found North End's backline static once more.
But a heavy touch gave goalkeeper Andy Lonergan time to scramble off his line and make what appeared to be a fine reflex save despite the assistant referee signalling a goal kick.
Preston responded with a chance of their own in the 24th minute. Davidson delivered an inviting cross from the left and Barton flashed his header wide.
North End enjoyed their best spell of pressure in the five minutes before half-time and Parkin smashed into the side netting, but the home side were still greeted with boos at the half-time whistle.
Seven minutes into the second half North End came agonisingly close to levelling matters.
Iain Hume's low 25 yard drive received the faintest of touches from the outstretched Mannone before rolling agonisingly across the line.
The visitors sealed the points in the 72nd minute when Garcia pick-pocketed makeshift Lillywhites left-back St Ledger to leave substitute Barmby with a tap-in.
Preston almost had a goal back when a calamitous mix-up between Dawson and Mannone presented Parkin with a chance but a combination of the offending defender and goalkeeper saw off the danger.
Hull substitute Simpson hit the post in stoppage time with the goal at his mercy following another error, this time from Preston defender Craig Morgan.