ROB Hall curled home a fantastic free-kick to send Oxford United into the Papa John’s Trophy quarter-finals at Cambridge United’s expense.

The U’s had struggled to break down their Sky Bet League Two opponents, but the No 7 struck 16 minutes from time to put his side through.

Sitting third in the fourth tier, Cambridge were not just making up the numbers and matched their hosts as both sides made several changes.

It took a quadruple substitution from United boss Karl Robinson on the hour to shake his side into life and they eventually did enough, stretching their unbeaten run to nine games in the process.

Robinson’s first line-up for ten days included nine changes to the side that beat Burton Albion on January 2.

Elliott Moore and Sam Long, were the only players to retain their places, the latter moving inside to centre back, while Cameron Brannagan made his first start since October 10.

Mark Sykes partnered the former Liverpool trainee in midfield and Sam Winnall led the line, while Anthony Forde began at right back following Sean Clare’s loan move to Burton earlier this evening.

The Irishman was on set-piece duty and had a busy opening four minutes as United forced three corners.

Only the first one truly threatened Callum Burton, the Cambridge goalkeeper tipping over Moore’s header at the back post.

Winnall and Brannagan linked up after seven minutes as the midfielder scuffed wide from his teammate’s knock down, before Hall had a curling effort parried behind at the near post.

The visitors began to gain a foothold midway through the half and were arguably the better team until the break.

They had particular joy down the flanks, with Joe Ironside heading over and captain Paul Digby shooting straight at Eastwood following two crosses in quick succession.

Wingers Luke Hannant and Leon Davies were pushing high up, but it was one of United’s wide men who went closest before the break.

Dan Agyei received the ball from Sykes on the edge of the area and turned before shooting across Burton with his left foot, only to see his effort whistle past the far post.

United were again on the front foot in the half’s early stages, with Jamie Hanson shooting over from 15 yards seven minutes in.

But by the hour mark Robinson had seen enough and made four substitutions, bringing on Marcus McGuane, Liam Kelly, Mide Shodipo and Derick Osei for Brannagan, Hanson, Agyei and Winnall.

The changes jolted the U’s into life and Shodipo curled an effort just wide of the far post shortly after coming on.

United continued to force plenty of corners with little joy, but it took a moment of real class from a set-piece to break the deadlock.

Hall was fouled by Harry Darling 20 yards out and picked himself up to strike an excellent free-kick inside Burton’s near post.

Cambridge manager Mark Bonner responded with all five changes in the space of seven minutes, while Alex Gorrin replaced Sykes to shore up United’s midfield.

Harrison Dunk, one of the visitors’ substitutes, fired a warning shot with four minutes left as he beat Forde in the air, only to head wide.

Cambridge gave United more to think about in the closing minutes, but the hosts saw the game out.

Oxford United (4-3-3): Eastwood, Forde, Moore, Long, Obita, Hanson (Kelly 61), Brannagan (McGuane 61), Sykes (Gorrin 81), Hall, Winnall (Osei 61), Agyei (Shodipo 61).

Unused subs: Stevens, Taylor.

Booked: Kelly.

Cambridge United (4-4-2): Burton, Okedina, Darling, Cundy, Iredale, Hannant (Dunk 74), May (O’Neil 81), Digby, Davies (Knoyle 74), Knibbs (Worman 74), Ironside (Dallas 81).

Unused subs: Mitov, Taylor.

Booked: Davies, Darling.

Referee: Charles Breakspear (Surrey).