It was on New Year's Day last year that Juan Mata finally cracked after being substituted by Chelsea manager Jose Mourinho at Southampton. He had done his utmost not to react and, placid by nature, there was no kicking water bottles, but he was visibly distraught despite the consolatory efforts of Michael Essien behind him. Fast forward 16 months and there was an altogether different kind of substitution in the 81st minute of last Sunday's Manchester derby. After scoring and inspiring United to 4-2 win, he received a standing ovation and a pat on the back from Ryan Giggs. Manchester United midfielder Juan Mata turns away to celebrate after scoring against Manchester City . Mata had scored United's third goal during the 4-2 victory over their bitter rivals at Old Trafford last week . Mata looks dejected after being substituted by Chelsea boss Jose Mourinho last year at Stamford Bridge . Although he had been a popular figure at Chelsea, Mata could not convince Mourinho to keep hold of him . Louis van Gaal is finally getting the best out of Juan Mata. In his last five games, the Spaniard has performed better than he ever has in the Premier League: . Mata is performing at the peak of his powers . He is not surprised by the turnaround in his own, and the team's, fortunes — he began the season believing United could win the league this year with no European commitments. He told Sportsmail last May: 'If we take Liverpool as the example there you have a team who have fought all the way to the finish without the Champions League.' He was mocked for the optimism but if United beat Chelsea at Stamford Bridge they will be only five points behind the leaders. When David Moyes was manager, he and assistant Phil Neville had scouted Europe for the 'Mata-type player' they believed the team needed before it became clear United could get the real thing. When Louis van Gaal arrived, Mata took one step forward and two back. The early tinkering often meant he played in his favoured position behind the front two, but the three-man defence experiment undermined everything else the team did and results were poor. He ended up back where he had been at Chelsea under Mourinho — on the bench. Mata missed the football he had played earlier in his career at Valencia and under Andre Villas-Boas at Chelsea. The free spirit was being shackled and the only consolation was that others felt the same, none more so than Ander Herrera, the player he is closest to at the club. The two had won an Under 21 European Championship together with Spain where they had enjoyed a freedom of expression now denied them. Herrera, like Mata, was out of the side. Mata also missed London. When I interviewed him in 2012 before the Champions League final he insisted on meeting in a Kings Road cafe because it was where he felt most at home. Now he was in a mansion in Alderley Edge, south Manchester. Isolated and not playing. As United's fortunes changed on the pitch, however, so Mata's season has been saved. With Michael Carrick now planted in front of a back four, the side has the balance to allow its creative players to thrive. Mata is not in his favoured No 10 position but he is also comfortable on the right. 'I can come inside on my left foot and see the whole of the pitch in front of me,' he says. Mata enjoys a close friendship with fellow Untied midfielder and Spain international Ander Herrera (right) Mata scores the second of his two goals against Liverpool at Anfield this season, a stunning overhead kick . It is the same left foot Giggs joked about with him when he joined, saying he was glad to see him arrive but unhappy that he no longer possessed the best left peg at Old Trafford. The relationship with Giggs is healthy, as is the one struck up with Wayne Rooney. Both were players Mata admired before moving to England. As well as the bond with Herrera he is close to David de Gea — all three of them live on the same street. De Gea is another with whom Mata played in that Under 21 European Championship success in Denmark in 2011. Having been part of the 2010 World Cup-winning squad, Mata's willingness to step back down to the Under 21s says a lot about his character. The open letter he wrote to Chelsea fans when he left the club — against advice that it was not the best way to ingratiate himself with his new supporters — also spoke volumes. A Chelsea fan holds a sign to pay tribute to Mata, who earned himself a hero's reputation in west London . Mata never wanted to leave London but now he loves the countryside surrounding Manchester. It reminds him of his home in Asturias, and that more than makes up for not being in the capital. Life there was good under Villas-Boas. 'He trusted me to play and he wants to play attractive, fun and winning football,' he said, revealing a fondness for someone whom Mourinho held in far lower esteem. Mata never banged on the manager's door when he fell out of favour at Chelsea. Mourinho never struck him as a man whose mind could be changed. He has always preferred to do his talking on the pitch. It has not always been easy but he is back at Chelsea on Saturday and there has never been a better time to make a lasting statement. Mata gets ready to play a pass during a club training session at the Aon Training Complex on Friday .
Despite his status as a firm fan-favourite during his first two seasons at Chelsea, Juan Mata could not do enough to impress Jose Mourinho.
Mata was sold to Manchester United in January 2014 for a £37m fee.
It took some time for the midfielder to settle at Old Trafford but now he has.
United travel away to Chelsea in the Premier League on Saturday.