As quickly as the last second win at Reading on day one will have lifted Derby County on to cloud nine, they were swiftly brought back to earth with a resounding bump at home to Leeds on Saturday afternoon.
Second best in virtually every area of the pitch, the Rams were taught a footballing lesson by Marcelo Bielsa's United, who on this evidence and that displayed in beating Stoke last week, must be fancied for a solid promotion tilt.
For the Rams, it's very much back to the drawing board, as a performance that was disorganised and again lacking creativity saw them well beaten and boss Frank Lampard scratching his head as to how he'll instil more belief into his team.
Heads will no doubt drop after this, but if some better-fitting pegs in the holes can be found by Lampard with the players at his disposal, there remains promise that his newly-constructed side can still provide plenty to shout about.
Derby had the first opening as Harry Wilson and new boy Martyn Waghorn caused problems and when the ball fell to Mason Mount six yards out he was unable to turn the ball home under pressure. Waghorn would otherwise have a quiet and frustrating afternoon on his Rams bow.
But it was United who went in front barely a minute later. Mateusz Klich was given too much space 25 yards out and he was able to place his shot past Carson and into the corner of the net.
Gjanni Alioski was less successful with an effort from a similar distance soon afterwards, but Derby would get level on 12 minutes in some style.
Tom Lawrence was fouled just outside the penalty area on a bright run forward, and from the free-kick, Lawrence himself smashed a dipping and swerving effort which beat keeper Bailey Peacock-Farrell through sheer pace although the keeper should arguably have dealt with it somehow.
But this pulsating game was to take another twist on 22 minutes. Alioski got some space down the left and floated in a superb cross which found Kemar Roofe whose perfectly placed header looped over Carson and into the net.
Sammy Saiz was proving a tricky character and broke forward to shoot straight at Carson on 28 minutes, before the game settled into a relative lull before the break despite the Rams' best efforts to put pressure on the United defence. Instead, the visitors stood firm while the likes of Richard Keogh and Joe Ledley continued to hold things together in Derby's defensive areas.
The break arrived with Leeds deservedly in front.
Bradley Johnson replaced the struggling Ledley at half-time, more solidity needed in front of the back four than Ledley had been able to provide.
And a goal nearly arrived straight away as Lawrence broke forward and found Mount but his mis-hit shot across goal just evaded Waghorn who was inches away from making contact.
Then Craig Bryson couldn't get a firm touch on a Lawrence cross on 54 as the Rams continued to look more lively.
At the other end, Carson then produced a superb point-blank save to deny Roofe his second, the rebound falling to Luke Ayling whose shot was deflected over the top by the excellent Tomori.
But it wouldn't be long before the third came, as Roofe received the ball in the penalty area and produced an exquisite turn to beat his man before hammering high into the net at Carson's near post.
And it was 4-1 three minutes later, as Pablo Hernandez got free on the right and his cross was met by Alioski who powered it past Carson from six yards out.
Ayling was just wide from distance on 71 as Leeds searched for a fifth, Alioski having fluffed his lines when through on goal moments earlier with an attempted chip that went horribly wrong.
Mount shot weakly at Peacock-Farrell as Derby desperately sought some kind of way back into the game, but they were being frustrated at every turn by the visitors, who saw the encounter out with few further scares to take a convincing three points.
Derby: Carson, Wisdom, Forsyth, Tomori, Keogh (c), Wilson (Josefzoon 61), Mount (Bennett 75), Waghorn, Lawrence, Lowe, Ledley (Johnson 46)
Subs not used; Roos, Forsyth, Marriott, Pearce
Leeds: Peacock-Farrell, Ayling, Douglas, Cooper (c), Roofe (Bamford 79), Alioski, Saiz (Baker 86), Hernandez, Phillips, Berardi, Klich (Shackleton 72)
Subs not used: Blackman, Roberts, Jansson, Harrison
Ref: Peter Bankes
Star Ram: Fikayo Tomori