Jed Wallace opened the scoring in the 20th minute, David Connolly made it two six minutes later and, after Andy Wright had been sent off, Patrick Agyemang wrapped up a 3-0 victory six minutes before the break.
Southend have made their best start to a season in 23 years and share top billing with Oxford.
The Shrimpers defeated Northampton 2-0 at Roots Hall today thanks to Anthony Straker (38) and Freddy Eastwood (62).
Oxford lead the table on goal difference after a 3-1 victory over Torquay.Striker James Constable was instrumental in Chris Wilder's side claiming their third league win in a row, scoring a superb 62nd-minute goal and laying on the third for fellow substitute Asa Hall (78).
More top news
A man who murdered his ex-girlfriend was violent and paranoid. Colin Dymond strangled and stabbed Sarah Pollock in her Bournemouth flat.
Simon's Blog - Trees That Look Like Other Things
Friday night's forecast for the east of the region