Wayne Rooney struck an injury-time penalty against League One Sheffield United to spare the blushes of Louis van Gaal at Old Trafford.

Van Gaal, criticised by the home fans for his substitutions, was heading for an eighth goalless draw of the season until substitution Memphis Depay drew Dean Hammond into a foul and Rooney rammed in the spot-kick as he continues to close on Sir Bobby Charlton’s goalscoring record.

Depay dramatically spun up in the air after contact from the Blades defender but replays show he was caught on the shin.

Wayne Rooney fires home the winning penalty that sent Manchester United through to the FA Cup fourth round

The 30-year-old celebrates his winner as the home side broke Sheffield United’s hearts at the death at Old Trafford

Memphis Depay was adjudged to have been fouled in the box by Sheffield United midfielder Dean Hammond 

The Dutch winger theatrically throws himself into the air after being caught by Hammond late on at Old Trafford

Under-pressure United boss Louis van Gaal waves to the fans after his side’s victory in the FA Cup third round

It was pure relief for the Dutchman whose side managed just two shots on target in the evening FA Cup third tie.

Disgruntled supporters chanted the name of Ander Herrera as he was replaced after an hour and Marouane Fellaini sarcastically cheered when he went off later – the fans wanted him gone long before.

But they failed to create anything of substance until Anthony Martial’s shot was blocked by Chris Basham late on.

Van Gaal hasn’t had a good record in domestic cup competitions and his side had failed to score against lower league MK Dons, Cambridge United and Middlesbrough in the past 18 months.

The Dutchman took no risks against The Blades – but that was the problem.

His line-up looked strong, just three changes from the team that beat Swansea 2-1 in the Premier League, but they lacked spark against a side ninth in League One.

Manchester United left back Cameron Borthwick-Jackson (left) tackles Paul Coutts during the FA Cup third round clash

Louis van Gaal walks towards the tunnel after watching his side fail to find the net during the first half at Old Trafford

Rooney looks to bend the ball over the wall but his free-kick was easily dealt with by the League One outfit 

Sheffield have beaten Aston Villa, Southampton and West Ham from the Premier League in recent years and they cleverly allowed Van Gaal’s men to have 70 per cent possession and tried to hit them on the break.

The slippy conditions, the result from a continuing torrential downpour, played into the underdogs hands as well.

Rooney, who has responded well to being dropped at Stoke on Boxing Day, enjoyed his old-fashioned battle with Neill Collins but faded the longer the game went on. He is still good at sticking penalties away but United don’t get much else for £250,000-a-week.

The conditions did make for some terrific shoulder charges and sliding tackles. One tackle by David Edgar dumped fans’ favourite Herrera on his backside but referee Jonathan Moss waved play to delight the traditionalists.

The first goalkeeper to be called into any action was Manchester’s David de Gea, tipping over a stinging attempt from the edge of the box by Conor Sammon after 19 minutes. But even that wouldn’t have counted with the striker called offside.

Rooney responded by dribbling around the other goalkeeper, George Long, but went too wide in the process and his subsequent cross was blocked by the visitor’s defence.

Manchester United fans have been cheesed off most of the season by the ponderous nature of their side’s play, particularly when coupled with poor results.

The last two games had been a little better, a 0-0 draw with Chelsea followed by the Swansea win, but the first-half on Saturday was another step back with Sheffield United, ninth in League One and 48 places below Manchester United in the league pyramid, looking more organised.

Chris Smalling attempts to getaway from Conor Sammon as the duo embarked on a physical battle at Old Trafford 

The Scotsman looks to chest the ball down and create an attack with United’s Daley Blind closing him down 

Their manager Nigel Adkins had named an unchanged team and would have been delighted by his players. As usual, Van Gaal stayed in the dug-out taking notes. His side bossed possession, 70 per cent, but went nowhere with it.

His best and most dangerous player in the first-half was Matteo Darmian whose delivery on the overlap was regularly top drawer. In contast, Juan Mata didn’t seem to get on with the drippy traditions.

Herrera did try his arm at creativity after 35 minutes with a pass slipped into Rooney but again it just skidded through a little too strongly for the United captain and Long came out bravely to smother. Daley Blind then tried to clip a pass into Herrera but the ball bounced off the Spaniard with a poor first touch.

Nigel Adkins shouts out instructions to his Sheffield United players during a wet encounter in Manchester 

Former Manchester United boss Sir Alex Ferguson was in the stands to watch the Red Devils in the FA Cup third round

You could sympathise with Van Gaal wanting to sign more players in January even if he has already spent £260million since succeeding David Moyes. Incidentally, £25million winger Memphis Depay was on the bench after flopping so far at Old Trafford.

Manchester United haven’t won the FA Cup for 12 years – too long for a club of their size and prestige. Yet there seemed little urgency, even the half-time talk on in-house television station MUTV was one of frustration that the manager was taking so little risk.

There did seem to be some emphasis on shifting the ball a little quicker in the second half but the final ball was too often woeful.

As the clocked towards the hour mark without a single shot placed on either target for either side, Sheffield United fans found their voice and mockingly chanted towards the Premier League superpower: ‘Are you Wednesday in disguise’.

Van Gaal threw on Jesse Lingard and Depay to try and give his side a spark. But there was discontent that it was two creative players Mata and Herrera who made way rather than one of the deeper-lying midfield players, Bastian Schweinsteiger or Marouane Fellaini. Pointedly, Herrera’s name was chanted by the Stretford End as he trudged off.

United’s players cut frustrated figures during the clash, which saw home supporters ironically cheer their side 

Bastian Schweinsteiger (right) is closed down by Chris Basham and John Brayford as the away side pressured their opponents 

Thousands of home supporters left early due to their frustration and missed Rooney’s match-winning injury time goal 

When Depay had a pop at goal from 25 yards midway through the second half, there was ironic cheers from the home support. It wasn’t aimed at the substitute but the lack of action beforehand. The attempt went wide nonetheless as the search for a shot on target continued.

That wait finally ended after 66 minutes when Sheffield’s Chris Basham launched a daisycutter than De Gea had to get down to and gather.

Manchester United finally registered their first on-target effort, Long saving equally comfortably from Matteo Darmian after 69 minutes.

Fellaini made way for Andreas Perreira in the home side’s final change.

It wasn’t quite the kitchen sink that Manchester threw in the final stages. But Martial had a shot charged down, then Depay pounced on a slight slip by John Brayford and took Hammond on one-on-one.

The rest is now history – and Manchester United are in the hat for round four. 

The Manchester United captain (left) nicks the ball away from Sheffield United goalkeeper George Long

The England international was unable to find the target and the away side managed to clear their lines 

The Sheffield United players look dejected (above) as Depay lays on the ground after going down in the penalty area (below)