Chelsea secured a crucial 1-0 win over Manchester United courtesy of a late winner in their Premier League clash at Old Trafford.
A tame game appeared to be meandering to an underwhelming conclusion when, after 87 minutes, Mata confirmed his status as Chelsea's outstanding player this season by firing towards the bottom corner with a shot that took a deflection off Phil Jones.
United reacted badly to the late setback and Rafael lost his head when kicking out at David Luiz and earning a red card, even if his opponent hardly covered himself in glory when smiling to himself as he dramatically clutched his leg on the floor.
The win moves Chelsea into third place, one point ahead of Arsenal having played a game fewer than the Gunners and three ahead of Tottenham, who Chelsea face at Stamford Bridge on Wednesday.
United made five changes with Wayne Rooney dropping out of the team and Anders Lindegaard given a rare chance in goal. Meanwhile, Chelsea fielded nine players who featured in the Europa League semi-final win over Basel.
It was a rather makeshift XI for the champions, particularly given the midfield brought together Anderson, Tom Cleverley and Phil Jones, and United struggled in the early stages of the match at Old Trafford.
As early as three minutes into the contest, Chelsea could have taken the lead. Mata and Victor Moses exchanged passes on the edge of the box before the Spaniard floated a gorgeous ball across for the unmarked Demba Ba, who got under the ball and sent it over the bar.
United, lacking Chelsea's level of incentive, carved out a number of half-chances, Cleverley firing wide on the half-volley after Robin van Persie chested a cross from Antonio Valencia into his path, but Chelsea's superior energy and application gave them the edge in the first half hour.
After 14 minutes they hit the woodwork when Oscar took the ball on a mazy run and fired in a low shot that Lindegaard deflected onto the base of the post. Another surge forward saw Mata lay the ball off to Moses on the edge of the box but the forward lifted his shot high into the stands.
However, United finished the first half the stronger side. First Ryan Giggs prised open the defence with a lovely pass for Van Persie, who after bisecting the two centre-backs manoeuvred the ball just wide of the post with his first touch. He in turn teed up Giggs for a volley that flew wide and Van Persie then saw a firm header clasped by Cech just before the break.
The second half was a turgid affair, which only sparked to life towards its conclusion. After Frank Lampard only narrowly failed to drop a cross onto the head of the unmarked Mata, Rafael saw his low centre turned into the side netting by the leg of Branislav Ivanovic.
Still, a goalless draw looked on the cards until Mata inspired the late winner three minutes from time. Ramires laid the ball off to Oscar and when he switched it quickly to the Spaniard, Mata arrowed a shot towards the bottom corner with an inadvertent touch from Jones beating Lindegaard in the United goal.
In a febrile final few minutes, Rafael was given a card as he went after Luiz near the corner flag and lashed out at his compatriot, chopping him to ground. Referee Howard Webb had no option but to send the right-back off, even if the sight of Luiz having a smile to himself was a strange one.
After a brief flurry of action, it was Chelsea who secured the victory that puts them in pole position to claim a place in the Champions League for next season.
MAN OF THE MATCH
Juan Mata (Chelsea) - Who else? Decided the game with his late inspiration leading to the winning goal and was head and shoulders above anyone else on the pitch.
MAN UTD: Lindegaard 6, Rafael 5, Vidic 6, Evans 7, Evra 6, Jones 6, Anderson 5, Valencia 5, Cleverley 5, Giggs, 6, Van Persie 6. Subs: Buttner 6, Rooney 6, Hernandez N/A.
CHELSEA: Cech 6, Azpilicueta 7, Ivanovic 6, Luiz 6, Cole 6, Ramires 6, Lampard 6, Moses 5, Mata 8, Oscar 6, Ba 6. Subs: Torres 6, Ake N/A.