Manchester - Manchester United manager Louis van Gaal was forced to defend both his tactics and squad management following a disjointed 1-0 home defeat by Southampton in the Premier League.
Substitute Dusan Tadic's 69th-minute goal earned Southampton a first victory at Old Trafford since January 1988, which allowed Ronald Koeman's side to climb above United to third place in the table.
Victory was the visitors' reward for a disciplined and intelligent display, but United misfired badly in attack, failing to muster a shot on target in a home league game for the first time since a 0-0 draw with Arsenal in May 2009.
On that occasion, the draw was enough to give United the league title, but Sunday's defeat left them with 37 points from 21 games -- the same amount as Van Gaal's hapless predecessor David Moyes had mustered at this stage last season.
Koeman suggested that United were having trouble adapting to Van Gaal's preference for a three-man defence, opining that "they have difficulties to build up with three centre-backs".
But Van Gaal, whose side have taken six points from a possible 15, rejected the claim and argued that Southampton had been "lucky" to avenge their 2-1 loss to United in December.
Asked if United had struggled to bring the ball out of defence, he replied: "I don't think so, because we were the dominating team. You have seen that today (Sunday). That for me is not any question."
Van Gaal also had to explain his decision to omit Radamel Falcao from his 18-man squad, having selected 19-year-old striker James Wilson ahead of the Colombia international.
With Luke Shaw, Daley Blind and Angel di Maria playing after injury, Van Gaal said he needed defensive and midfield cover on the bench and had plumped for Wilson over Falcao "because I know I want speed in attack".
In the end, Van Gaal threw Marouane Fellaini on as an auxiliary striker, but Juan Mata squandered late chances to equalise when he failed to convert a pair of excellent opportunities created by Blind.
Falcao may get a recall at Queens Park Rangers next weekend, with Van Gaal revealing at the end of a spiky press conference that Robin van Persie had sustained an ankle injury.
Southampton's campaign appeared to have come off the rails following a run of four straight defeats in early December, but they have now won four of their last five matches, defeating Arsenal and United and drawing 1-1 at home to leaders Chelsea.
Seven of the 14 players who featured at Old Trafford were not even at the club last season and Koeman believes his side are acquiring the belief required to mount a sustained challenge for a Champions League place.
"We know that we have a strong team and it was important in the end of December that we got a point against Chelsea and the three points against Arsenal," said the former Netherlands international.
"That's always what you need if you are not a big club and you have to play against a big one -- that belief in the players, and not (being) afraid about the name, not afraid about the stadium.
"We have 11 clean sheets now (actually 10) in 21 games. If we keep the spirit and we know what we have to do in our organisation, we can keep in front in the table."
Tadic was booked for whipping off his shirt after scoring with the game's only shot on target -- following up after Graziano Pelle had hit the post -- and Koeman said that he would speak to the Serbian winger about the matter.
"I don't like that," Koeman said. "Because it's a yellow card and a stupid fault is your second (yellow card), and it's a red card.
"When it's the last minute of the season and you have qualified for European football, then it's no problem. But keep that shirt on."