The two Manchester clubs will meet in the semifinals of the English League Cup after both pulled clear in the second half to beat lower-division opponents in the last eight on Wednesday.
City stayed on course to win the competition for a third straight season after Raheem Sterling scored twice after halftime in a 3-1 win at third-tier Oxford that proved tougher than expected for the Premier League champions.
United scored all of its goals after the break to earn a 3-0 win over Colchester, which arrived at Old Trafford in ninth place in the fourth tier and defended stoutly before Marcus Rashford's opener on the counterattack in the 51st minute.