Crawley Town recovered from 3-0 down to 3-2 but ultimately lost in a thrilling finish at Brisbane Road.
Reds looked out of the game at half-time after a slow start led to a lacklustre first half display.
They went 2-0 behind after just 11 minutes through goals by Sam Dalby and Paul McCallum which was added to by McCallum on the stroke of half-time.
But Reds refused to roll over during the second half and forced an exciting last few minutes after an own goal and a goal by Enzio Boldewijn made it 3-2.
Reds named an unchanged team for the third match in a row.
Orient fielded two players making their full league debut: striker Sam Dalby and Teddy Mazague who have replaced Jay Simpson and Robbie Weir, who are on the bench.
Dalby celebrated his first start in perfect style by giving his side the lead in only the fourth minute when he volleyed in a cross from the right by Nigel Atangana.
The hosts doubled their lead just seven minutes later from a free-kick by Michael Collins which was crossed into the area by Gavin Massey before Paul McCallum slid the ball into the net.
Reds were slow to maske an impact in the game but finally built an attack after 22 minutes when Jordan Roberts tried to find Enzio Boldewijn who was in a dangerous position but the ball was palmed away by keeper Alex Cisak.
Crawley produced a shot on target on the half hour when James Collins volleyed a cross from Roberts, but the attempt flew straight to Cisak, who comfortably held.
Orient took a 3-0 lead into half-time with another goal by McCallum from the penalty spot after Roberts brought down Massey.
Reds made a substitution at the start of the second half, bringing on central defender Joe McNerney for Andre Blackman as Crawley switched to 3-5-2.
Crawley pulled a goal back nine minutes into the second half when pressure from Reds forced Mezague to put Lewis Young’s cross into his own net.
Crawley looked more dominant and went close when Roberts found Collins in the area but he volleyed over the bar.
Orient had a decent shout for a penalty turned down when McNerney brought down Massey.
Rreds continued to press in search of a second goal as collins chipped over and Boldewijn had efforts cleared by the defence.
Boldwewijn then made it 3-2 with 13 minutes to go with a composed goal, receiving a ball over the top, he rounded keeper Cisak before side-footing in.
Josh Payne then saw a free-kicked tipped over the bar by Cisak as Reds kept pressing for a late equaliser.
REDS: Morris, Young, Payne, Connolly, Smith (capt), Roberts (Bawling 65), Blackman (McNerney 46), Yorwerth, Clifford, Collins.
Unused subs: Beeney, Davey, Yussuf, Djalo, Henderson
ORIENT: Cisak, Judd, Hunt, Parkes, Kennedy, Massey, Weir, Atangana, Bowery, McCallum, Dalby (Bowery 55)
Unused subs: Collins, Weir, Palmer, Simpson, Koroma, Erichot
REFEREE: Trevor Kettle
ATTENDANCE: 4,486 (295 away)
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