Sanchez, who joined United over neighbour and Premier League leader Manchester City, said he was "thrilled to be joining the biggest club in the world". Alexis Sanchez has hit out at former Arsenal players who "cause damage" with their media speculation, and insisted he always gave 100 percent for the club.
While Sanchez entered the final six months of his contract at Arsenal, Mkhitaryan was 18 months into a four-year deal at United. "He's a really good player and I think he will be a good addition, really good".
Mkhitaryan made a modest start to his United career and did not start a Premier League game in nearly three months after he was substituted at half-time during his full debut against Manchester City.
"The chance to play in this historic stadium (Old Trafford) and to work with (United manager) Jose Mourinho was something I could not turn down".More news: Coquitlam family grieves death of teen bystander killed by stray bullet
Mkhitaryan, 29, moved to Old Trafford from Borussia Dortmund in the Bundesliga for 26.3m pounds in July 2016.
"I would like to say a heartfelt thank you to Manchester United players and staff and especially the fans for your love, passion and support".
Should Manchester United manager Jose Mourinho opt to stick with his current formation following the signing of Sanchez, one of Marcus Rashford or Anthony Martial looks set to suffer.
Another added: "Welcome to the Theatre of Dreams Alexis Sanchez".More news: Oscar nominations: Here's behind the scenes with Priyanka Chopra
The 29-year-old Chile global will reportedly become the highest-paid player in Premier League history following the deal which sees Henrikh Mkhitaryan heading in the opposite direction. "He's a special player and the sort that doesn't come around that often, and I'd say United's hopes of winning their fourth European trophy have just got a lot more likely".
Both clubs have officially announced about the transfers.
Giroud's probably frustrated about a lack of playing time, and a move to an Auba-less Dortmund might solve that problem for him, but it doesn't solve the problem of Arsenal no longer having Olivier Giroud.
The Home Office will not discuss individual cases but Sky Sports News understands neither player will have to leave the United Kingdom in order to meet any extension requirements. I would like to play with everyone, to start training very soon.More news: Alexis Sanchez joins Manchester United from Arsenal; Henrikh Mkhitaryan moves to Emirates