While the defense deserves a fair amount of blame any time a team concedes three goals—and United's defense looked extremely weak on this night—poor performances by first-year Reds Juan Mata and Marouane Fellaini certainly contributed to their ineptitude in finding the back of the net.
Although a poor performance by a player will always bring a negative response, the play of Mata and Fellaini was even more disheartening due to their improved run of form as of late.
United fans were optimistic of Mata linking up with Rooney as he did vs. West Ham, and they looked for Fellaini to continue improving in the defensive midfield role he has played in.
However, neither of those things happened.
Mata's and Fellaini's poor nights started with their inability to finish chances. The Spaniard could only muster up a weak shot when he had a chance to score, and the Belgian couldn't quite test the keeper on a half-volley from point-blank range.
Past that, however, the duo was unable to perform its respective roles: offensive creation and strong defensive play.
Despite having a respectable 84 percent pass success rate, Mata was unable to put his teammates in positions to score, failing to create even one key pass throughout the course of the match and producing just one accurate cross from five attempts. In addition, Mata proved to be extremely flimsy and weak on the ball, getting dispossessed twice.
Mata's disappointing performances might have some United fans wishing the club would've spent the money used on him to purchase a versatile box-to-box midfielder, which is a far greater need for the team than a primarily attacking player.
Just as Mata was disappointing on the offensive end, Fellaini failed to really be a defensive stalwart in the middle of the park. The Belgian should be credited for winning 75 percent of his aerial duels but was poor otherwise. He had only one interception, four less than Wayne Rooney, and he failed to record a tackle, blocked shot or clearance.
He also showed little discipline, amassing three fouls and a yellow card which could've definitely been a red.
Fellaini, who played in a more advanced role at Everton, has really only been a defensive player for United in terms of his positioning, as he's played way too skittishly and scared for someone who stands at 6'4" (and probably 6'8" with that afro of his).
United fans will be patient with Mata, who is not playing his best football at the moment but seems to be trying his best and is fully committed to United's mission.
However, Reds fans could soon grow extremely tired and agitated with Fellaini. Aside from playing poorly this season, Fellaini has often been detrimental to the squad with his reckless behavior. With his three fouls against Manchester City, the midfielder now has 12 in his past four games.
Ultimately, United fans are still hoping that Fellaini and Mata can pan out at United, and they still want to give them their full support.
But at some point, they have to be given a reason to.
Stats via WhoScored.com unless otherwise noted.