Campbell is spending a year on loan with the Greek team, and his goal demonstrated his undoubted talent. The Costa Rican skipped inside from his starting position in the right and bent a beautiful curled effort beyond the goaltender. Arsenal had dealt a blow to their rivals without even taking the field.
The defeat was a new low for United and David Moyes. For Arsenal fans, it offered a tantalising glimpse of a player who has been with the club for almost three years without making a single senior appearance.
Due to work permit issues, Campbell was forced to spend his first two years at the club away from Britain. A relatively quiet loan period at Lorient was followed by a more successful spell at Real Betis. However, it's in Greece that he has really found his feet.
Campbell has been a hit at Olympiacos. His goal against United was his eighth strike this season. Prior to Christmas, he enjoyed a prolific run of five goals in seven games.
Campbell's impressive form has led to speculation that Olympiacos would like to make the loan deal permanent. The Metro report that talks between Arsenal and the Greek side have already begun.
However, speaking to Matt Barlow of The Daily Mail, Campbell underlined his determination to become an Arsenal player. He still retains an affinity for the club that plucked him from Costa Rican football three summers ago:
They showed an interest in me when I was moving to Europe but I have been an Arsenal fan since I was a child and that’s why I chose them.
There are a lot of good players in Costa Rica. Many of them like me think only of being a footballer and it was very exciting when some of the most important clubs in the world started to show interest in me.
As soon as Arsenal came, I wanted to join them and I believe I am ready to play for Arsenal next season.
Campbell has not given up on his dream of playing for Arsenal's first team. His form for Olympiacos suggests he deserves a chance. As he himself says, "I know I have the capacity to play there. I am only waiting for the opportunity. With hard work I know I can get there."
His confidence is warranted. This is an established international footballer. At 21, he already has 30 full caps and eight goals. This summer, he will play in the World Cup against the likes of England and Italy. If Arsenal are determined to sell him, they should certainly wait to see how he gets on in Brazil before agreeing on any price.
However, Arsene Wenger should give serious consideration to keeping Campbell around. His speed and shooting ability make him an intriguing option either as a central striker or on the flank. He'd certainly have more of an impact than the lightweight Ryo Miyaichi.
The exciting forward now has a valid work permit that allows him to play in the Premier League. It would be great to see him finally use it.