A week that started with a knee injury to Casper Ankergren and continued with the national humiliation of Scott Carson was ended yesterday by an error of judgement from David Lucas which cost Leeds their second league defeat of the season.

Lucas saw his weak clearance lobbed into an empty net by Cheltenham Town forward Steve Gillespie with four minutes remaining at Whaddon Road, ensuring a result which left United baffled.

The former Sheffield Wednesday keeper had been a peripheral figure for three-quarters of the match, and had not been asked to make a serious save until Dean Sinclair's high delivery towards the edge of his box caused sudden uncertainty among Lucas and his defence.

Lucas appeared at the edge of his box and scuffed a header straight to the feet of Gillespie, who held his composure and guided a controlled chip into the corner of United's goal. Leeds have worked late goals to their advantage this term but, with 86 minutes gone, Gillespie's opportunistic finish left no chance of a reprieve.

Cheltenham's victory was an astonishing outcome for a team who, until yesterday, were bottom of League One with two wins from 16 games.

The Gloucestershire club have been cannon-fodder this season and their manager, Keith Downing, was waited patiently for a result capable of providing his squad with impetus. He could not have asked for better than the win that came their way yesterday.

United's defeat, however, distorted the facts of a game which, in the home of National Hunt racing, Dennis Wise's team should have won at a canter.

Lucas will rue the manner of Gillespie's late winner, but his rash header was only partially responsible for the expensive loss of three points which should have been added to United's League One total.

Leeds produced 19 efforts on goal and had enough opportunities to settled the fixture several times over before Cheltenham successfully chanced their luck during the final minutes.

Jermaine Beckford hit the crossbar in the first half and had a header disallowed by a marginal offside decision in the second, summing up a day when both the prolific striker and his club seemed destined to leave Whaddon Road empty-handed.

Wise has rarely been asked to count the cost of missed chances this season, but that failing did arguably greater damage to Leeds yesterday than Lucas' error. So intent was United's manager on finding a winning goal that he boldly reverted to a 4-2-4 formation with 17 minutes remaining, fielding Beckford, Tresor Kandol, Mark De Vries and Tore Andre Flo in attack. It is doubtful, given that strength of personnel, whether a goalless draw would have satisfied Wise any more than a 1-0 defeat.

His side were considerably better than Cheltenham, who had little intention of playing their way through United's defence and were no more adept at employing direct tactics. Had Downing's backline given way once, it is possible that an avalanche of goals would have followed.

But United's string of missed chances combined with the minimal pressure on Lucas and his defenders suggested - as is so often the way - that an unpleasant surprise might be waiting around the corner. Though Cheltenham had offered nothing up front before Gillespie's goal, it almost felt as if his strike had been coming.

For all Leeds' dominance, Wise left Whaddon Road acutely aware of problems that require attention before Port Vale arrive at Elland Road a week tomorrow.

United were productive in attack, yet their crosses into Cheltenham's area were consistently inaccurate and wasteful of valuable possession. Their passing, meanwhile, was ambitious to the point of hopeful, often punctuated by 40-yards balls which bypassed their target. Still, it was difficult to be critical of a team who might have had the result sown up by the time the interval arrived.

It aided Cheltenham's cause that Beckford's afternoon became a mixture of misfortune and inaccuracy.

The striker was denied in the 38th minute when he spun clear of Shane Duff inside Cheltenham's box and crashed a shot against the crossbar, and on three occasions the hosts' clean sheet was spared by the margin of a foot.

Beckford drove a volley narrowly over Shane Higgs' goal in the ninth minute, and placed a lob to the wrong side of the post after running onto Kandol's flicked header six minutes after half-time. When Beckford flashed another chance over an open goal in the 66th minute - an opportunity which might have been take more easily with a header - it seemed possible that the match might be heading for an unlikely ending.

But Cheltenham's victory did not come without a moment of controversy, and the decision to deny Beckford the opening goal in the 77th minute.

The forward was first to react after Douglas' free-kick rebounded off the body of Higgs, but his cushioned header into the net was adjudged to have come from an offside position. It was a close call, and one which favoured Cheltenham more than Downing could have imagined.

Lucas promptly damaged his shoulder after conceding a corner in a challenge involving him, Manuel Rui Marques and Cheltenham substitute Guy Madjo, and ramifications were serious.

The keeper collected the resulting set-piece safely under his bar but was visibly in pain as he launched a wayward throw in the direction of Douglas. Sinclair was first to the loose ball, and his looping pass to the edge of United's area forced Lucas to commit himself with a headed clearance which Gillespie exploited brilliantly.

His strike brought the first league win of Downing's reign at Whaddon Road, and bowed United for only the second time this season. Suddenly, top by Christmas is not quite the formality is seemed.