The Magpies, who strolled to the title the last time they competed at this level, came to life in the second half but could only create a couple of openings in front of goal, although they did have two strong penalty shouts turned down.
It means a sixth successive home win for Fulham over their opponents at Craven Cottage to kick off the new season, and a sixth clean sheet in their last eight opening fixtures.
In an opening 45 minutes largely devoid of any real chances, the biggest talking point arrived 35 minutes in when Ryan Tunnicliffe blocked aside Matt Ritchie's left-sided cross with his outstretched arm.
Referee Simon Hooper, who had earlier called Grant Hanley's challenge on Sone Aluko inside the box correctly when waving play on, decided against pointing to the spot to the dismay of the travelling fans.
United fielded five debutants from the off, and it told in the first half as a large hold on possession counted for very little with no attempts on target for the visitors.
Smith's goal then arrived right on the brink of the interval, as he glanced Tom Cairney's corner into the back of the net after being left unmarked 12 yards out.
Visiting boss Rafael Benitez, one of two Champions League-winning managers in the Championship this season, decided against any changes at the break but did move Ritchie onto his favoured flank.
That meant Vurnon Anita switching out to the left, a move that almost paid instant dividends when the Dutchman picked out Ritchie just six yards out, only for the subsequent shot to be blasted into the legs of David Button - United's best chance of the match.
With the Magpies enjoying the lion's share of possession, the Whites were having to settle for hitting their opponents on the counter and so nearly profited when Smith headed down for Aluko.
Hanley was again at the centre of a penalty call when making contact with his opponent, but the referee once more waved played on to the relief of the United defender.
Ritchie and Scott Malone both came close for their respective sides soon after - the latter in particular creating a big opening only to scuff his left-footed shot wide of goal when played through.
Floyd Ayite very nearly settled things when creating a chance from nothing after turning and shooting in the box, although Fulham's hard work almost counted for little when Ritchie's shot was blocked by Kalas's hand in the box.
For the third time in the game Hooper declined the shouts for a penalty and allowed play to continue, meaning a big opening-day win for Fulham on home soil as they saw the remainder through.