Matt Lockwood scored a penalty as Leyton Orient continued their 100 per cent start to the season.
Lockwood scored Orient's goal
The goal, scored five minutes before the break, came after defender Shelton Martin was penalised for a clumsy challenge on winger Shane Tudor.
Darlington almost equalised but Glyn Garner saved from Simon Johnson.
Lee Steele and Craig Easton both struck the crossbar for Orient, while Quakers substitute Akpo Sodje wasted two good chances to equalise late on.
Darlington: Russell, Martis, Hutchinson, Clarke (Webster 75), Valentine, Wainwright, Dickman (Ndumbu-Nsungu 75), Appleby, Logan, Johnson, Wijnhard (Sodje 45).
Subs Not Used: Duke, Peacock.
Leyton Orient: Garner, Barnard, Mackie, Zakuani, Lockwood, Tudor (Easton 67), Simpson, McMahon, Keith, Steele (Echanomi 81), Alexander.
Subs Not Used: Dolan, Morris, Miller.
Goals: Lockwood 41 pen.
Ref: J Moss (West Yorkshire).