Braces from Gavin Tomlin and Britt Assombalonga saw Southend end 10-man Torquay's unbeaten home record.
Tomlin rifled through Martin Rice's legs for the first, before Assombalonga ran clear to finish on the break.
The Watford loanee doubled his tally as he headed in Kevan Hurst's cross and former Torquay loanee Tomlin tucked away a fourth after the break.
Ryan Jarvis netted a consolation for the Gulls, who then saw Lee Mansell red-carded for a foul on Assombalonga.
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Torquay United manager Martin Ling told BBC Radio Devon:
"Southend made us look very poor on the day. That's down to me as the manager, and also the players and the coaching staff, we're all in it together.
"It isn't good enough and the players know that.
"Let's be honest, we're Torquay. There's no money in the coffers to go and get four or five players and replace them all, so we'll stick with the group and the crowd need to stick with us."
Southend manager Paul Sturrock told BBC Essex:
"We've got some good players and everyone fits into the jigsaw puzzle of the team. I'm very pleased.
"The front two have been so exciting. They ran them ragged today.
"(Britt Assombalonga) was starting to worry me. He was having that superstitious stuff about what boots to wear and everything else. I'm glad he's got back on the scoresheet again.
"He's always there or thereabouts, sneaking about the box. He's not just a finisher, for a young boy he's got a great career down the line."