An emphatic first-half performance saw United run in three goals through Danny Welbeck, Chris Smalling and Fabio.
When substitute Adnan Januzaj added a fourth five minutes into the second half a rout looked on, however goals from Lam Ka-Wai and Alex Tayo Alkande brought the hosts back into the match before Jesse Lingard restored United's three-goal advantage.
David Moyes gave starts to youngsters Michael Keane and Ben Amos, with Wilfried Zaha and Ashley Young supporting lone striker Welbeck.
The Premier League champions started well and after Anderson had missed two chances, they took the lead in the 16th minute through Welbeck.
Michael Carrick delivered a perfectly lofted pass to Young inside the area and the forward's volley deflected onto the post, but the rebound fell to Welbeck, who volleyed home first time for his third goal in pre-season.
Six minutes later, the visitors doubled their lead through Smalling.
The defender rose unmarked inside the penalty area to meet a Tom Cleverley cross from the right, and his header was too powerful for Wang Zhenpeng to keep out.
It was all one-way traffic, and after 26 minutes Fabio added a third as United's dominance continued to pay off.
Zaha had managed to keep a wayward Patrice Evra cross in play before delivering a disguised pass into the path of the Brazilian full-back, and the 23-year-old took the ball in his stride before driving a low shot under Zhenpeng and into the bottom corner.
Moyes made three changes at the break, introducing Lingard, Januzaj and Alex Buttner - and within five minutes Januzaj was on the scoresheet. Buttner was released down the left-hand side and delivered a perfect cross onto the head of the 18-year-old, who made no mistake from six yards.
Kitchee gave the home fans something to cheer about in the 53rd minute as Wai pulled a goal back - the captain picking the ball up on the left, drifting past Carrick and unleashing a left-footed shot into the top corner that Amos could do nothing about.
And they pulled a further goal back just after the hour through forward Alkande.
After soaking up pressure from United, a long ball out of defence found the Nigerian and he cut in from the right before turning away from Buttner to side-foot past Amos.
Lingard sealed the win for United with their fifth goal 10 minutes from time. The 20-year-old found himself alone with four defenders for company before working the ball onto his right foot and unleashing a curling effort into the Zhenpeng's top corner.
