Leaders Arsenal, meanwhile, spurned an opportunity to move four points clear after drawing 2-2 at Southampton, but Liverpool tightened their grip on fourth place with a superb 4-0 defeat of derby rivals Everton.

Mata started the game at Old Trafford, three days after making a �37.1 million ($61.2 million, 44.8 million euros) move from Chelsea, as former United striker Ole Gunnar Solskjaer returned to his old stomping ground as Cardiff manager.

Last season's top scorer Robin van Persie was also included in United's starting line-up, after seven weeks out with a thigh strain, and the Dutch striker broke the deadlock in the sixth minute.

Mata found Ashley Young with a raking pass and when his cross was headed against the bar by Antonio Valencia, Van Persie headed in at the second attempt after his initial header was parried by goalkeeper David Marshall.

Young added a fine second in the 59th minute, cutting in from the left flank and arrowing a drive into the bottom-right corner, before Wayne Rooney made his return from injury as a substitute for Van Persie.

United manager David Moyes was left to reflect on a satisfactory night, saying: "We kept a clean sheet, scored a couple of goals, got a couple of players back from injury, and gave Juan Mata his debut."

Mata, who claimed an assist for Young's goal, told the BBC: "The win was very important for the team. It was very exciting for me. The fans are unbelievable. The lads welcomed me very well."

On United's chances of a top-four finish, he added: "We will try until the end. We will never give up."

United, who had lost three of their previous five home league games, remain six points below the Champions League places, but they inched to within 12 points of Arsenal after the London club's slip-up at St Mary's.

Bidding to move four points clear of second-place Manchester City, Arsenal fell behind in the 21st minute when centre-back Jose Fonte headed in a left-wing cross from Luke Shaw.

The visitors sprang to life early in the second half, equalising through Olivier Giroud's clever back-heel and going ahead when Santi Cazorla drilled home, only for Adam Lallana to sweep in an equaliser two minutes later.

Arsenal's push for a late winner was undermined when midfielder Mathieu Flamini was sent off for a studs-up lunge at Morgan Schneiderlin.

Arsene Wenger's side are now at risk from City, who will take over at the top if they win at Tottenham Hotspur on Wednesday, while Chelsea could draw level with Arsenal if they win at home to West Ham United.

Reflecting on the matches awaiting his side's rivals, Arsenal manager Wenger said: "They have difficult games as well, and we took at least a point.

"It's not enough but considering the situation at half-time, we have to be content with it."

Liverpool moved three points clear of fifth-place Spurs and four points above sixth-place Everton with a memorable 4-0 victory in a one-sided Merseyside derby at Anfield.

Steven Gerrard's 21st-minute header from Luis Suarez's corner broke the deadlock and a quick-fire brace from Daniel Sturridge put the game beyond Everton before half-time.

The England striker finished coolly from Philippe Coutinho's through ball in the 33rd minute before deftly lobbing Everton goalkeeper Tim Howard from the edge of the area two minutes later.

Suarez raced clear to add a fourth early in the second half, while Sturridge squandered an opportunity to complete his hat-trick by blazing a penalty over the crossbar.

"It's a massive victory over rivals close to us," said Liverpool manager Brendan Rodgers.

"If you look at Everton, they've only conceded 11 goals away from home before tonight (Tuesday) and for us to get four and to maybe have had a few more is very pleasing."

France midfielder Yohan Cabaye, who is reported to be on the verge of a move to Paris Saint-Germain, was absent for Newcastle United as Alan Pardew's side recorded a 0-0 draw at Norwich City.

Both sides finished with 10 men after Newcastle striker Loic Remy and Norwich midfielder Bradley Johnson were shown straight red cards following a late altercation.

Goals from Jonjo Shelvey and Chico Flores gave Swansea City a 2-0 win at home to relegation-threatened Fulham, while improving Crystal Palace climbed to 14th after an early Jason Puncheon goal saw them beat Hull City 1-0.