The rivalry
Manchester United and Arsenal are great footballing rivals. In addition to the tense relationship between one of the most important cities in northern England and the southern metropolis of London, the rivalry between the two clubs amplified after the Premier League was founded in 1992.
In the 1990s and at the turn of the millennium, the Red Devils and the Gunners often battled each other for league titles and other domestic trophies. The matches between them were also, for many years, battles between two the league's great managers - Sir Alex Ferguson and Arsene Wenger.
A heated build-up
There had been several incidents between Ferguson and Wenger during previous clashes of their teams. This time, Ferguson caused tension before the match when he took a shot at Wenger's record in recent years, saying he would "not have allowed" such a barren run without trophies.
Arsenal's previous trophy at the time was winning the Community Shield in 2005. On the contrary, Manchester United started the 2011/2012 season as the reigning Premier League champions. In 2011, the Red Devils won their 12th league title (out of a total of 13) in the Ferguson era.
Manchester United had started their title defence by winning the first two matches of the season, while Arsenal drew in the opening match and lost their second-round clash to Liverpool, thus they were looking for their first win of the league season.
A crucial missed penalty
The match kicked off in front of an almost sold-out crowd at Old Trafford. Manchester United opened the scoring in the 22nd minute when Danny Welbeck headed the ball past Arsenal's goalkeeper Wojciech Szczesny.
The Gunners had a chance to level the scores five minutes later when they were awarded a penalty for a foul on Theo Walcott by Johnny Evans. However, David de Gea, who was playing in goal for the fourth game in a row after signing from Atletico Madrid in the summer, correctly guessed the direction of Robin Van Persie's penalty kick.
Just a minute later, Ashley Young, another United's summer signing, got to the ball at the other end of the field. He took it under control, shifted it onto his right foot and curled a shot into the top corner to score his first goal for the Red Devils.
In the 41st minute, Wayne Rooney scored his 150th Manchester United goal. And it was an outstanding goal from a free kick. He rolled the ball to Young, who stopped it, changing the angle for Rooney to curl it around the defensive wall into the top corner.
Arsenal pulled a goal back in injury time at the end of the first half when Andrey Arshavin and Tomas Rosicky combined on the edge of the penalty area, Van Persie allowed the ball to run through to Walcott, who shot through De Gea's legs. It was Arsenal's first league goal of the season. At half-time, the score was 3-1 to United.
The hat-trick hero
It took almost 20 minutes of the second half before another goal was scored. It was in the 64th minute when Rooney netted the ball again from another free kick. He ran the same set-piece routine as for his earlier goal with the same result – a wonderful goal.
After that came a flurry of other goals. Three minutes later, Rooney assisted an unmarked Nani to lob Szczesny. In the 70th minute, Park Ji-Sung scored with a low shot to the far post. Then Van Persie reduced the deficit for Arsenal in the 74th minute.
Shortly after, Arsenal's Carl Jenkinson received a second yellow card and was sent off, meaning the Gunners had had a player dismissed in each of their first three games of the season.
After another foul, this time in the box, Rooney completed his hat-trick in the 80th minute from a penalty spot. The final and tenth goal of the match was scored by Ashley Young again with a beautiful curling shot to the far post.
The final score was 8-2 to the Red Devils and Manchester United had inflicted Arsenal's heaviest defeat since 1896. The star of the match was Ashley Young, who himself scored two goals and assisted three. Wayne Rooney scored his sixth Manchester United hat-trick (of his eight in total for the Red Devils).
Manchester United thus started the 2011/2012 season with three wins in a row. After that, they continued to do well, but at the end of the season, they lost the title in the last round in a thrilling long-distance title battle with another great rival, Manchester City.
Despite a poor start to the season, Arsenal eventually finished in a respectable third place. The Gunners' top scorer Robin Van Persie won the Premier League Golden Boot scoring 30 goals. However, in the summer of 2012, he was transferred to one of the club's most bitter rivals... Manchester United. The rest, they say, is history.