John McGreal's men did their 5,000 travelling fans proud as the U's made their first visit to Old Trafford, with the lowest ranked team left in the competition stymieing the illustrious hosts – whose boss Solskjaer marks a year in charge on Thursday – through doggedness and discipline in the first half.

But just as Colchester supporters began to dream of adding to the Carabao Cup scalps of Crystal Palace and Tottenham, Rashford scored a fine opener on the break just 15 seconds after Jackson had a shot at the other end.

The Colchester man turned a Mason Greenwood cross into his own goal as salt was quickly rubbed into the wound, with Martial settling the tie from a smart first-time Rashford pass.

The England international, one of four survivors from Sunday's draw with Everton, had two early attempts from free-kicks in a bright start. Colchester goalkeeper Dean Gerken could not deal with the second one, just about jumping on the ball before Juan Mata could pounce.

Rashford then hit a thumping 25-yard effort over as he pushed to open the scoring, but the visitors were holding firm thanks to a sturdy backline the alertness of Gerken.

Andreas Pereira was looking most likely to unpick the Colchester defence and sent a fine lofted ball over to Rashford, only for the forward to fluff his lines. Still fuelled by that frustration, his next attempt went out for a thrown-in.

The fact goalkeeper Gerken was booked for time wasting in the 39th minute and Colchester's impressive support celebrated a corner four minutes later underlined the uphill battle faced by the visitors.

But while it remained goalless, they could dream.

Callum Harriott showed quick feet to rifle a low attempt wide of Sergio Romero's goal from the resulting corner and it took a last-ditch Luke Shaw challenge to halt a dangerous counter-attack soon after.

Martial went mightily close with a long-range strike in stoppage-time but Colchester fans were on their feet in anticipation when Jackson raced down the right and saw a shot from a tight angle saved by Romero in the 51st minute.

But within seconds they were dealt a gut punch.

Romero rolled the ball out to Nemanja Matic, who sent Rashford scampering down the left with a ball over the top. The 22-year-old smelt blood, cut across the box and showed great composure to dart away from defenders before lashing home in front of the Stretford End.

Cohen Bramall attempted to level, but United would grab a second in the 56th minute.

Greenwood has impressed in front of goal in recent matches and this time provided a teasing cross from the right that Jackson was only able to turn into his own goal. Rashford, who was ready to pounce at the far post, applauded the 18-year-old's efforts.

The match was over as a contest in the 61st minute. Mata superbly lifted the ball over to Rashford, whose first-time ball back across goal was turned in by Martial.

Substitute Brandon Williams had attempts blocked either side of a saved Greenwood shot and Mata struck wide as United looked to add gloss. Gerken superbly denied Harry Maguire's header as Colchester went out with a valiant display.