Manchester United edged through to the FA Cup Fourth Round thanks to late strikes from Jesse Lingard and Romelu Lukaku in a frustrating affair with Championship high-flyers Derby County.
Lingard, in the form of his life, pulled off a stunning first-time effort from outside the area to break the deadlock on 84 minutes.
Anthony Martial combined well with Lukaku on the counter in stoppage time to ensure of the victory and make it two games, two wins and two clean sheets to kick-off 2018.
Team changes galore
David De Gea, Phil Jones and Nemanja Matić were awarded much-deserved rests in five changes made by José Mourinho, as Sergio Romero made his sixth appearance of the season - every one of those in cup competition.
Marcos Rojo and Anthony Martial dropped to the bench with strong 2015-16 duo Chris Smalling and Daley Blind the preferred centre-backs and Marcus Rashford leading the line.
Henrikh Mkhitaryan, who could be on his way out of the club this month, was also recalled to the attack, making just his second start in 15 outings, alongside in-form pairing Juan Mata and Jesse Lingard.
The visitors' starting line-up confirmed Gary Rowett's predominant focus on the Championship this season, where his side are vying for automatic promotion to the Premier League and currently sit in 2nd place.
So much so, that more changes were made than the hosts including three in the back line; with Andre Wisdom, Alex Pearce and Marcus Olsson coming in for Chris Baird, Curtis Davies and Craig Forsyth.
George Thorne came in for Bradley Johnson to partner Tom Huddlestone in a midfield pivot, while Sam Winnall started up front instead of usual first choice, David Nugent.
United academy graduate Tom Lawrence made his Old Trafford return as part of an attacking three behind the striker, at the expense of star man Matej Vydra, who had to settle for a place on the bench.
Dominant United struggle for breakthrough
The tone of the first-half was set early on, as Paul Pogba's intricate skill helped him lay off Jesse Lingard inside the box, who could only shoot over the bar against the club United sent him on loan to in the 2014-15 season.
This match could've been seen as a last chance for Henrikh Mkhitaryan to fight for his place, playing in his favoured central position against lower league opposition, but once again he didn't have the best of halves.
More crosses were massively evading their targets, and he sent the opposition on a counter-attack with a disastrous pass backwards eventually finding it's way to Sam Winnall on the edge of the area - luckily for Mkhitaryan, his shot was skewed well wide.
Derby enjoyed a good spell mid-way through the first period and were growing in confidence on the break, but Chris Smalling was a stand-out performer and made numerous good one-on-one challenges to clear the danger.
Marcus Rashford was presented with the best chance of the half as a fortunate bobble gave him space to pull the trigger towards goal, but he fired his shot just over the bar - the shot should've hit the target, and if it did, would've given the hosts a deserved lead.
Scott Carson's first terrific free-kick stops came on 21 minutes after Juan Mata was floored by Alex Pearce whilst trying to complete a one-two 20 yards out, and the subsequent set-piece was tipped wide for a corner before it could find the top left corner.
The away side's only challenging attempt on target came straight afterwards, as Johnny Russell's cross from the left found the head of Marcus Olsson, and Sergio Romero had to work to direct the effort over the crossbar.
Mkhitaryan eventually got a cross right with 10 minutes of the first 45 left, directing an in-swinger from the left into a crowd of men in the Derby area, and Marcus Rashford rose highest to direct his header onto the post.
Straight after going the closest to breaking the deadlock, the young Englishman went close with another header, this time getting on the end of a Mata cross to head straight into the hands of Carson in goal.
As the end of the first-half approached, United were set up in a 2-1-7 formation with Ander Herrera sat in front of Smalling and Blind while Luke Shaw and Victor Lindelöf became impromptu wingers.
The half's final opportunity asked for another top Scott Carson save. Paul Pogba was brought down 30 yards away from goal and very nearly spectacularly found the top left corner with his resulting free-kick - it would've been special, but the score remained level.
Late Lingard stunner saves Mourinho's blushes
It caused no surprise in the stands that Henrikh Mkhitaryan was brought off at the break for Romelu Lukaku, who missed his Everton homecoming on New Years Day after a nasty head injury on his last Old Trafford outing against Southampton.
There would also be no shock if that turns out to be Mkhitaryan's final stand, another lacklustre showing.
Derby County made a very strong start to the second-half and were clearly growing in confidence; but still living dangerously as Mata, Lukaku and Pogba all had shots saved, blocked and fired narrowly wide respectively five minutes after the restart.
Marcus Rashford's pace was causing the Rams' defence real issues down the channels, and José Mourinho opted for more speed with 20 minutes to go as Anthony Martial replaced Juan Mata.
Meanwhile, Matej Vydra, who has scored 14 goals in 22 Championship matches this term, replaced frontman Sam Winnall at the same time as Gary Rowett looked to build on his outfit's solid performance.
Rashford certainly wasn't having the best of luck on the night, hitting the post for a second time in the 71st minute after releasing a fierce right-footed strike across goal from the right side of the box - Scott Carson was beaten.
The Red Devils hit the woodwork again minutes later from Romelu Lukaku's header, but a goal wouldn't have counted anyway as the big Belgian was ruled offside.
With 10 minutes left on the clock, Derby weren't offering anything going forward as they desperately held on to the draw as it was the same old story for United - wastefulness in front of goal and brilliantly goalkeeping making lives difficult.
Scott Carson pulled off another save to deny Jesse Lingard from the edge of the area before Paul Pogba trickled an awful effort wide on the rebound.
It looked set that Mourinho's men were going have have to travel to Pride Park for an unwanted replay with seven minutes to go, but the hottest man currently on the block at Old Trafford had other ideas.
The ball went astray outside the left side of the area and who else but Jesse Lingard was there to pull off an unbelievable first-time strike to bend the ball away from the 'keeper and into the top right corner - Carson was brilliant on the night but there was no stopping that.
That opener flattened out the game as United looked comfortable in possession, but Romelu Lukaku struck in stoppage time to double the lead and seal progression to the Fourth Round of the FA Cup.
Manchester United were sitting back under slight pressure and launched the ball up to Lukaku, who took it down superbly. He played it to Martial on the right who put it back inside, and the no. 9 only had to slot it past Scott Carson inside the box to make it 2-0.