Vietnamese cup holders Ninh Binh have seen their squad depleted in recent months following their controversial withdrawal from V.League 1, and had not played a competitive fixture since progressing past Churchill Brothers in the round of 16 in May.
Nevertheless, the home side were unbeaten in this competition and coach Van Sy had spoken confidently about his team's chances ahead of kick-off.
However, in Juan Belencoso, Kitchee possess the top scorer in this season's AFC Cup, and the Spaniard lived up to his reputation by breaking the deadlock in the 28th minute.
Lok Fung Ngan doubled the advantage for the Hong Kong outfit four minutes into the second half, but Suleiman Oladoja hit back just before the hour mark to reduce the deficit to one goal.
Le Van Thang found the net to keep the difference between the sides to a single goal after Xu Deshuai had stretched the margin once again, but the final word fell to Beloncoso, who scored his 10th goal of the tournament in stoppage time to send Kitchee into next week's home leg firmly in the ascendancy.
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