A red card to Chris Dagnall proved to be a turning point as Orient were beaten 3-1 at Valley Parade.
Having fallen behind in the first half to a tap in from Billy Knott, substitute David Mooney levelled things with 15 minutes to go but there was barely time for Orient to regroup before Dagnall was given a straight red - a decision that looked harsh on the O's forward.
The home side cashed in on the extra man immediately as goals from Jon Stead and Billy Clarke killed any hopes of an Orient fightback.
Mauro Milanese made just one change from the side that beat Crewe last weekend with the suspended Romain Vincelot making way for Jack Price. On the bench, Gary Woods missed out with a knock to his thumb meaning Charlie Grainger was recalled from his loan at Farnborough to enter the squad.
The home side were direct in their approach early on and forced the first chance after five minutes when Orient failed to clear a ball from the right which fell for Mark Yeates who dipped a volley narrowly over the bar as the Bantams looked to seize the early initiative.
The O's coped well with the direct approach as Scott Cuthbert and Nathan Clarke competed well in the air with Jon Stead and Billy Clarke and Milanese's side created their first chance with 11 minutes gone as the Italian duo of Andrea Dossena and Gianvito Plasmati combined well before the latter dragged a shot wide.
It wasn't particularly easy on the eye as Bradford went from back to front and Orient struggled to retain the ball but the home side looked the more dangerous early and Clarke was next to go close when he glanced a free-kick from Yeates just past the post.
As the half ticked on, Dossena entered the book for a late tackle and referee Darren Handley called in the O's skipper Clarke to issue a warning to the left back as he reacted angrily to the decision.
It looked like Orient had weathered the Bantams storm as they showed signs of better cohesion going forwards but they mounted a late charge as Clarke went close twice before Yeates blazed a shot narrowly over and Legzdins dived bravely at the feet of Stead to keep it 0-0.
The warning signs were there and sure enough with three minutes of the half remaining, the home side grabbed the lead. Stead latched on to a ball inside the penalty box and turned well to square for Billy Knott who tapped home from close range.
Jobi McAnuff replaced Bradley Pritchard at the interval as Orient went in search of a way back into it and had an appeal for a penalty five minutes into the half when Dossena's cross appeared to be blocked by an arm but again nothing was given by Handley.
Orient were certainly brighter in the second period and the Bantams pressure was less relentless but still Milanese would have wanted his side to create more chances going forwards as he threw David Mooney into the fray in place of Plasmati.
Parkinson's side still posed a threat going forwards as Andy Halliday fired a warning shot against the crossbar with 20 minutes to go via a hand from Legzdins before the game sparked into life with 15 minutes remaining.
First of all Orient levelled it when substitute Mooney did brilliantly to capitalise on a mistake in the Bantams back four and race through on goal before keeping his cool and slotting home.
It looked as if it set things up nicely for an Orient onslaught with time running out but the game was turned on its head just two minutes later when Dagnall was shown a red card for a late tackle in front of the dugout. It looked harsh but referee Handley wasted not time in brandishing a red.
The dismissal knocked the wind out of Orient as the home team grabbed the lead again when Billy Clarke collected a cross from the left and fired above Legzdins.
The home side were in a ruthless mood and the tie was killed a minute later. Legzdins - who had impressed throughout - hit a clearance straight at Stead who remained cool to round the O's 'keeper and bury it.
BRADFORD: Pickford, Darby (C), Meredith, Davies, Liddle, Clarke, Knott, Yeates, Stead (Hanson 89), McArdle, Halliday (Zoko 80)
Subs: Sheehan, Kennedy, Routis, Mottley-Henry
Goals: Knott 42, Clarke 79, Stead 81
Bookings: Liddle 45, Darby 56
ORIENT: Legzdins, Omozusi, Cuthbert, Cox, Clarke (C), Wright, Pritchard (McAnuff 45), Dagnall, Price, Plasmati (Mooney 65), Dossena
Subs: Grainger, Sawyer, Baudry, Batt, Lee
Goals: Mooney 75
Bookings: Dossena 28,
Red: Dagnall 76
Attendance: 12,489 (308)