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Three goals in eight minutes either side of half-time helped condemn Margate to a fourth successive defeat in Vanarama National League South at Hartsdown Park on Saturday.
City had looked the sharper side for much of the first half but the game was goalless until Godfrey Poku raced clear to fire them in front six minutes before the break.
Worse was to follow for Blues when, from the last action of the half defender Robbie Cundy bundled home City's second, and 90 seconds after the restart Tom Winters claimed a third to kill the contest.
Sub Mike Fondop - a former Gate target - made it 4-0 just three minutes after coming on and then, after Gate midfielder Lewis Taylor had seen red, the former Billericay striker claimed a second to complete the rout.
Worringly for Gate boss Nikki Bull his side have not won in the league since beating Hemel Hempstead 2-1 at home on October 8 and have conceded 15 goals in their four defeats since while scoring just once. It was the second successive home game they had conceded five.
Gate keeper Jon Henly made his home debut while skipper Luke Moore returned after suspension. Striker Kane Rowland was given his first start while Aaron Tumwa and Harry Phipps dropped to the bench.
City had recorded back-to-back wins going into the game and they began confidently going close to opening the scoring in the eighth minute when Josh Ashby's shot was deflected just wide after a flowing move.
From the corner Jefferson Louis scrambled the ball home only for the linesman to flag for an infringement.
City's passing, particularly in the final third was slick, but Gate gradually weathered the storm and began to get a foothold on the game with Chris Sessegnon making several breaks down the right.
The midfield worked hard to close City down and after that promising start the visitors were largely restricted to shots from outside the box.
James Roberts whizzed one wide of the far post after good passing between Ashby and Winters on 27 minutes, and two minutes later another quick break by City ended with Ashby blazing high and wide from 20 yards.
Gate had their moments, winning three corners while Moore blazed over but with six minutes of the half remaining visiting skipper Poku pounced on a stray pass to break clear and beat Henly inside his near post.
Gate probably deserved to go in only one down but when they failed to clear a Tom Winters free-kick Cundy was on hand to force the ball home.
Boss Bull replaced Rowland with Jermaine Osei at half-time but any hopes of a comeback were ended on 47 minutes when the Gate again failed to deal with a free-kick and Winters cut inside to fire home from close range.
Gate were unhappy with the award of the free-kick but they could have few complaints about the result as City continued to create chances almost at will.
Reece Fleet had already dragged a shot wide from 12 yards when substitute Mike Fondop got in behind the Gate defence to rifle the fourth on 64 minutes.
The big striker should have made it 5-0 soon after when he fired wide when through and Gate's day went from bad to worse when Lewis Taylor was sent off after collecting a second yellow for a foul on Jonny Giles with 16 minutes remaining.
City's Winters should then have done better than head over and Henly also saved well from Roberts but with three minutes remaining Fondop rubbed salt into Gate wounds by adding his second after Poku had cut the ball back.
Margate: Henly, Sessegnon, B Johnson, M Johnson (Foster 80mins), Parry, Fitzsimons, Taylor, Moore, Barrington (Phipps 73mins), Rowland (Osei half-time), Osborn; Subs: Tumwa, Kallmeier.
Oxford City: Belford, Poku, Grant (N'Gathe 73mins), Ashby (Davies 73mins) Henderson, Cundy, Giles, Fleet, Roberts, Louis (Fondop 60mins), Winters; Sub: Ofosu.
Attendance: 493