In beating the U's 2-1, with goals from David Mooney and Kevin Lisbie either side of Jabo Ibehre's equaliser, it is the first time in the O's history they have started a season with five straight wins.
Russell Slade's side are two points clear of Wolves, who maintained their unbeaten start to the season with a 3-1 victory at Port Vale.
The shock of the day was at London Road where Peterborough surrendered their 100 per cent start, losing 2-0 to Crawley.
Gary Alexander scored both goals for Town, whose day was soured when Michael Jones was sent off late on.
Behind the leading trio of teams at the top of table come three sides on nine points in Brentford, Rotherham and the MK Dons.
The Bees were held to a goalless draw at home to Carlisle, but for the Millers and the Dons, they both recorded 1-0 wins at Notts County and Sheffield United respectively.
Kieran Agard scored Rotherham's only goal in the 37th minute, while Anthony Kay netted just three minutes from time against the Blades, who had Fabian Brandy dismissed in injury time.
County are now one place off the foot of the table and three points above Coventry, who are on minus two after drawing 1-1 at Shrewsbury.
Callum Wilson put the Sky Blues in front after just four minutes with his sixth goal of the season, but Town levelled three minutes into the second half courtesy of Tom Bradshaw's third in as many games.
The day's biggest winners were Swindon who hammered Crewe 5-0 at the County Ground where Ryan Mason, one of four players signed on loan from Spurs over the summer, scored a 25-minute, second-half hat-trick.
Nile Ranger started the rout in the 34th minute before another Spurs loanee in Massimo Luongo added the second just prior to the break.
Preston enjoyed a comfortable 3-0 win at Walsall, ending the Saddlers' 16-match unbeaten run at the Banks's Stadium where Joel Byrom, Chris Humphrey and Lee Holmes netted the goals.
Tranmere moved out of the bottom four with their first league win of the season, a 1-0 success at Oldham, albeit in controversial circumstances.
Ryan Lowe scored a penalty in the fifth minute of injury time after he had been brought down by Oldham goalkeeper Mark Oxley, a decision that resulted in Latics manager Lee Johnson being sent to the stands for his protests.
The other two matches culminated in 1-1 draws, with Gillingham and Stevenage held at home by Bristol City and Bradford respectively.
At the Priestfield Stadium, Ade Akinfenwa gave the Gills a 22nd-minute lead, only for Marvin Elliott to haul City level on the stroke of half time.
At Broadhall Way, the visitors also had to come from behind, with Kyel Reid's fine free-kick cancelling out Greg Tansey's penalty opener.
Brentford 0 - 0 Carlisle
Colchester 1 - 2 Leyton Orient
Gillingham 1 - 1 Bristol City
Notts County 0 - 1 Rotherham
Oldham 0 - 1 Tranmere
Peterborough 0 - 2 Crawley
Port Vale 1 - 3 Wolves
Sheff Utd 0 - 1 MK Dons
Shrewsbury 1 - 1 Coventry
Stevenage 1 - 1 Bradford
Swindon 5 - 0 Crewe
Walsall 0 - 3 Preston
- Sports & Recreation
- Notts County
- Kevin Lisbie