Second half goals from Ben Whiteman and Danny Rose saw the O’s drop into the bottom two with a 2-0 loss at Mansfield Town.
After a goalless first half, the Stags broke the deadlock through Whiteman’s volley from just outside the box, before Rose bundled in a second at the back post to seal a fourth defeat on the spin for Orient.
The O’s made two changes from the side which lost 2-1 at Portsmouth, with Callum Kennedy and Sam Dalby restored to the starting line-up in place of Myles Judd and Nigel Atangana.
There was also a spot on the bench for defender Michael Clark who was recalled from his loan with East Thurrock United with injury ruling out Aron Pollock.
It was the hosts who started on the front foot with former Stag Nicky Hunt’s weak back pass allowing ex O’s loanee Shaquile Coulthirst to nip in. The ball then fell to Danny Rose but he shot wide under pressure from O’s goalkeeper Alex Cisak.
Cisak was by far the busier goalkeeper in the opening exchanges, and was forced into a strong save to deny Mal Benning after the Stags took a quick free-kick.
Ben Whiteman was next to an effort away on the O’s goal as he turned and shot from the edge of the box but fizzed it just over with Cisak at full stretch.
Chances were at a premium from that moment on, but on a rare forage forward for the O’s Hunt played in Gavin Massey whose cross-come-shot was drilled wide.
Cisak was forced into action once more and he did well to tip another Benning shot wide, before the Stags won a free-kick.
From that set piece the O’s failed to clear their lines and Rose fired just over the bar, and as the half entered the closing stages Orient won their first corner of the game.
Kennedy’s inswinging corner found the head of McCallum, but his effort was blocked by the Stags defence and eventually cleared.
No changes were made at the break by either side but Orient found themselves a goal behind with the half just three minutes old.
The ball fell kindly to Ben Whiteman just outside the area after the O’s had only half cleared a free-kick and he volleyed the ball past a helpless Cisak to break the deadlock.
It could have been two just moments later when Coulthirst struck the bar with a fierce effort from distance, however, the hosts did add a second with 56 minutes on the clock.
A cross from CJ Hamilton found Danny Rose lurking at the back post and he managed to fire in from an acute angle to give the O’s a mountain to climb.
Former Stag Ollie Palmer was already ready to come on before the goal, and before play restarted he replaced Dalby.
Steve Evans’ side remained on top after the second and Coulthirst flashed an effort into the side-netting.
The game entered the final 15 minutes and after a burst of pace for Palmer, he played the ball into Collins who in turn found Semedo. A viciously curling cross found the head of McCallum but the striker could only direct it over the bar.
Cisak was equal to another Whiteman effort as any chance of an O’s comeback continued to fade away, before the Aussie shot stopper blocked a Coulthirst effort.
A lengthy delay to the proceedings ensued late on after McCallum fell awkwardly on the edge of the box, and the day got worse for the O’s as he was forced off on a stretcher and was replaced by Victor Adeboyejo.
From the resultant free-kick, Kennedy struck the wall, before seeing his follow-up effort strike the outside of the post and with that went any chance of a late goal for the O’s as they fell to defeat.
MANSFIELD: Kean, Bennett, Benning, Collins, Pearce (c), Coulthirst (Arquin 90+5), White, Hamilton, Byrom, Whiteman (Baxendale 85), Rose (Green 74).
SUBS: Shearer, Hoban, Thomas, Hemmings.
GOALS: Whiteman (48), Rose (57)
BOOKED: Whiteman (82)
ORIENT: Cisak, Hunt (c), Mezague, Parkes, Kennedy, Massey, Moore, Collins, Semedo, McCallum (Adeboyejo 90+3), Dalby (Palmer 57)
SUBS: Sargeant, Clark, Judd, Atangana, Moncur.
BOOKED: Massey (53), McCallum (61), Hunt (73), Moore (80).
REFEREE: Graham Salisbury
ATTENDANCE: 3,925 (279 Orient fans)