Experienced striker Kevin Lisbie helped himself to two goals before Ian Goodison was dismissed for a tangle with the forward.
David Mooney missed the resulting penalty but Orient pushed on and secured a straightforward victory with Dean Cox and Shaun Batt adding late goals.
Darren Ferguson's Peterborough remain on the heels of Orient after a 1-0 home win at the expense of Shrewsbury.
With little to choose between the two sides it was Nathaniel Mendez-Laing's thumping 64th-minute effort that ultimately gave Posh the three points.
Third-placed Wolves lost ground on the top two after conceding a late equaliser to draw 1-1 at home to Coventry.
Leigh Griffiths put Kenny Jackett's side ahead midway through the second half as his shot went in under Joe Murphy for his eighth goal of the campaign.
But they could not hold on to claim the three points as substitute Aaron Phillips scored his first goal for Coventry with four minutes remaining.
Preston moved up to fourth after dishing out a 2-1 win over Peter Taylor in his first game as Gillingham's caretaker manager.
After an even first half at Priestfield Preston took control of the game by scoring twice in the opening eight minutes following the interval.
Keith Keane and Josh Brownhill were the scorers for Preston, who hung on for the points despite Danny Kedwell's 76th-minute header for the home side.
It was Bradford who surrendered fourth place to Preston after Phil Parkinson's side lost 1-0 at Crawley.
The hosts just about shaded the match and took all three points courtesy of Emile Sinclair's second-half strike.
MK Dons made heavy weather of beating 10-man Rotherham at stadium:mk before eventually running out 3-2 winners.
Michael O'Connor was sent off for Rotherham after conceding a penalty in first-half stoppage time that was tucked away by Shaun Williams.
The result seemed certain when Ben Reeves stabbed home from close range to double the Dons' lead before Rotherham came right back in to the game.
Lee Frecklington headed home Craig Morgan's 73rd minute cross with Tom Flanagan's own goal two minutes later drawing the visitors level.
But Karl Robinson's side showed great composure to find a winner which came courtesy of an 88th-minute strike from Patrick Bamford.
Sheffield United picked up just their second win in 16 league games after beating Port Vale 2-1 at Bramall Lane, with the win also taking Chris Morgan's side out of the relegation zone.
A 12th-minute Neill Collins header put the Blades in front before Adam Yates scored a fantastic equaliser on the stroke of half-time.
Michael Doyle scored the vital winning goal with a little under 15 minutes remaining to give United's fans a rare home success.
Brentford scored three times in the last 14 minutes to beat Colchester 3-1 at Griffin Park.
Magnus Okuonghae gave the visitors the lead four minutes in to the second half but goals from Marcello Trotta, George Saville and Kadeem Harris saw Uwe Rosler's side take the points.
Walsall beat 10-man Stevenage 2-1 with goals from Romaine Sawyers and Craig Westcarr.
Francois Zoko pulled one back for Stevenage but Lucas Akins' dismissal soon after put paid to any comeback.
Elsewhere, Byron Moore's stoppage-time penalty gave Crewe a 1-0 win over winless Bristol City whilst Adam Rooney's spot-kick was the difference as Oldham beat Carlisle by the same scoreline, ending the visitors' recent improvement under Graham Kavanagh.