City were eyeing the route back to winning ways, having drawn to Exeter City and losing to Salford in the past two weeks, but were bolstered by the return of Reece Staunton and top scorer Billy Clarke.
Leyton Orient: Vigouroux; Ling, Coulson, Happe, Widdowson, Cisse, Kyprianou, Wilkinson, Dennis, Brophy, Johnson
Bradford City: O'Donnell; P O'Connor, A O'Connor, Staunton, French, Wood, Sutton, Watt, Clarke, Donaldson, Samuels
Story of the match
The Bantams had the first opportunity of the game, as a switched ball from Elliot Watt found wing-back Connor Wood, but his effort on his weak foot sailed over.
City remained dominant in the opening fifteen, as a fortunate ball from Clarke took a deflection off Levi Sutton and found Wood in space once again, but this time his strike was low and wide.
That left flank remained Wood's territory, as he floated a handsome ball into the box but Clarke's header didn't have the power to threaten Lawrence Vigouroux.
Wood, once again, threatening, as his low ball found Clarke whose deflected cross had to be kept out by the Chilean shot stopper.
James Brophy presented the first opportunity of the game for Orient, as the winger did some tricky foot work to get past Anthony O'Connor and Tyler French, before French recklessly brought down Brophy on the edge of the box. The resulting free-kick was cleared.
A dull first half began to approach it's interval, before Clayton Donaldson flicked through to Austin Samuels but his effort was blocked for a corner. The following corner was poked towards goal by Paudie O'Connor, but kept out by Vigouroux.
Referee Sam Allison brought a lacklustre first half to a close, with Orient dominating the possession but yet to really test Richard O'Donnell, whilst the Bantams had enjoyed a few early opportunities but hadn't penetrated the goal as of yet.
A single swap at the break, as Connor Wilkinson was replaced by Jordan Maguire-Drew.
Leyton Orient came out fighting, as Brophy intimidated once again, meeting Louis Dennis' switching pass and producing a teasing ball across goal, which bobbled out for a corner.
McCall was forced into a change as Staunton was forced off of the pitch with a suspected hamstring injury, and on came Ben Richards-Everton.
City immediately forced an attack, as Clarke spotted Samuels in behind, but the loanee forward's strike was blocked for a corner.
The resulting corner ended in a scramble, as a few back and fourth headers ended with Donaldson, but his far post attempt was gratefully grasped onto by Vigouroux.
A second change for Bradford, as Clarke was replaced by youth graduate Kian Scales.
However the changes weren't enough for the Bantams, as a in-swinging free-kick from Maguire-Drew found defender Dan Happe in the six yard box, who glanced in the air and powered his header past the helpless O'Donnell to give the home side the lead.
The winning side next made a substitute as Jobi McAnuff came on for Harry Kyprianou.
Some nice footwork from Donaldson found Wood on the wing, but his cross was deflected by Sam Ling and Scales couldn't quite provide the penultimate touch.
Dennis made way for Josh Wright, who previously played for Bradford but departed on bad terms.
Heading towards the final ten minutes of the match, Leyton Orient won a free-kick on the edge of the Bradford box, but Maguire-Drew's effort frightened O'Donnell's goal, parrying against the side of the net.
The away side prepared a final throw at the dice, as Samuels exchanged for Dylan Mottley-Henry.
Into stoppage time, up stepped Watt for a corner but it ended in the comfortable hands of Vigouroux.
Embleton looked to waste time as Brophy was switched for Olatunji Akinola.
And it proved effective- as Allison brought a rather wearisome affair to a finale.
A rather uneventful and monotonous match, Leyton Orient edged out Bradford in a game which had just three shots on target all game.
The O's and Embleton will be the happier of the two with the three points, but performance wise it was a professional job. A game which saw the home side take their opportunity with a dominant Happe goal that was unstoppable from O'Donnell, before Orient put ten men behind the ball and simply ran down the clock.
In terms of the new five substitutes rule, Leyton Orient took advantage of it making four subs which proved pivotal. Maguire-Drew coming on was an inspired change, being fantastic in challenging a poor Bantams defence and providing the assist to the decisive goal. McAnuff and Wright also had promising games, both having a solid performance and doing the role required of them. Meanwhile with Bradford, there substitute bench is a huge problem.
No player on the bench for Bradford came on and had an impact, Scales was quiet and seemed to disappear at times, Richards-Everton was careless on the ball and fired it out of play rather than trying to find a man, whilst Mottley-Henry didn't really have enough time to alter the game.
But the lack of quality and depth in this City squad is worrying, with injuries dampening the squad, as Gareth Evans, Lee Novak, Kurtis Guthrie and now Staunton all absent, McCall has insisted he doesn't need to bring in signings but this squad is simply not good enough to match the ambitions of the club- as Bradford have now slipped to a measly 20th position in the league.
Furthermore, Bradford lacked creativity, with Wood and Clarke being the only outlets but squandered their chances early on. Donaldson and Samuels are capable goal-scorers but haven't received the opportunities which could have given the Bantams a chance to assert their dominance over the tie.
Stand out players
A game which lacked any individual moments of brilliance, Dan Happe was probably the man of the match. Comfortable and composed on the ball, he often carried it out of defence and transitioned the ball to the midfield with the hopes of creating something for his side. He also got the decisive goal which will prove pivotal in Orient's race for the play-offs.
In terms of Bradford, Connor Wood was unlucky to be involved in a defeat. Especially in the first half, the left-back continuously found space on his flank and created several opportunities which lacked the final finish.