Sam Smith at the double as Cambridge United beat 10-man Oxford United in the Papa John's Trophy

Sam Smith bagged a brace for Cambridge United as they triumphed 4-1 against 10-man Oxford United in the Papa John's Trophy, Group H game at the Abbey Stadium.

The striker pounced twice in the first half and Harvey Knibbs and youth-team player and debutant Kai Yearn netted after the break as the U's made Oxford pay after Luke McNally was sent off at the end of the first period.

The hosts definitely settled faster into their game. They were playing some very neat, possession-led football in an attempt to move their opponents out of shape, without quite being able to create any clear-cut chances.

That changed in the 16th minute when a corner from the left was met with a looping header by Adam May, which hung in the air before hitting the bar. The rebound dropped to young debutant Mamadou Jobe, who saw his attempt cleared off the line, and then Harvey Knibbs was similarly foiled.

Oxford had grown into the game, and had an impressive 10-minute spell.

Tyler Goodrham's 25-yard effort was met by strong hands by U's keeper Kyle Mckenzie-Lyle, who was making his first-team debut despite having signed last summer.

Nathan Holland cut in off the left wing and fired wide from the edge of the area, while Joel Cooper then had an attempt which was pushed out at full stretch by Mckenzie-Lyle.

In the 35th minute, Holland flashed a shot across the area which was easily dealt with by Mckenzie-Lyle, and the U's soon established full control again.

May put a great through ball for Smith to latch onto but the striker steered the chance wide from just inside the box.

They did not have to wait too much longer to take the lead though.

A superb delivery from a corner on the right by Ben Worman was met by the head of Smith at the front post and he found the back of the net.

United's cause was helped a minute later when McNally was sent off for a professional foul on Knibbs on the edge of the area, after the hosts' striker was played clear.

The subsequent free kick was deflected wide, but from the resulting corner, another superb delivery from Worman was flicked on by May at the near post and Smith was really alert with a neat finish to make it 2-0.

The hosts started the second half in a similar vain.

They were moving possession from flank to flank, seeking to draw out Oxford, but the best they had to show in the early stages was Jack Lankester's shot that was blocked at the front post.

In the 65th minute, Harrison Dunk dug out a cross that Smith met acrobatically but it was easily gathered by Oxford keeper Simon Eastwood.

The visitors went close to getting a goal back in the 66th minute, when Gatlin O'Donkor played in the overlapping Michael Elechi who thundred a shot against the post.

Oxford did reduce the arrears five minutes later.

With very little backlift, Dan Agyei curled a shot into the top corner from 25 yards.

Any nerves from United were settled in the 80th minute.

Debutant Liam Bennett hit a piledriver from 25 yards that was destined for the top corner before Eastwood tipped it over.

Another brilliant corner from Worman went to the back post untouched where Knibbs arrived to nudge the ball over the line to make it 3-1.

The hosts continued to flood forward at will, with Dunk, Worman and Knibbs all firing off target, while James Brophy was denied by Eastwood and Yearn had a chance deflected over the bar.

A memorable night for Yearn was capped off in the first minute of stoppage time.

Bennett delivered a low cross from the right, and the teenager nipped in ahead of the defender to sidefoot home to make it 4-1.

It capped a good display for United, who will be delighted by the performance of the team, especially their debutants.

Cambridge United: Mckenzie-Lyle, Bennett, Jobe, Digby, Dunk, Lankester, May, Weir, Worman, Smith, Knibbs.

Substitutes: Mannion, Williams, Brophy, O'Neil, Masterson, Beckett, Yearn.

Oxford United: Eastwood, Chambers-Parillon, Mousinho, McNally, Elechi, Johnson, Kane, Cooper, Goodrham, Holland, Agyei.

Substitutes: Stevens, Watt, Nosakhare, Anifowose, Smith, O'Donkor.

Referee: Sam Allison.

Sending off: Oxford United - McNally (professional foul, 45+2).