Published: 13:50, 10 November 2019
| Updated: 16:01, 10 November 2019
Substitute Ruel Sotiriou scored a stunning late winner to send Whites into the second round of the FA Cup on Sunday.
The loan signing from Leyton Orient had only been on the pitch three minutes when he fired past Southend keeper Nathan Bishop with six minutes to go at Crabble.
Victory was no more than Andy Hessenthaler's side deserved as they had created the better chances and might have doubled their lead when Jai Reason's chip hit the crossbar.
Dover boss Hessenthaler made just one change to the side which had drawn at AFC Fylde in the league the previous weekend and that was enforced with right-back Josh Passley missing out through injury.
Aaron Simpson switched flanks to replace him with Bobby-Joe Taylor playing on the left after recovering from his hamstring problem.
Midfielder Reason started despite reports ahead of the tie that he was suspended after collecting five bookings.
Southend, 22nd in League 1 after losing 14 of their 17 League 1 games, began on the front front, forcing a couple of early corners, the second of which gave home goalkeeper Yusuf Mersin the chance to make a confidence-boosting catch.
Dover's first real foray forward ended with Southend full-back Nathan Ralph making a vital interception as Jack Munns tried to get on the end of Taylor's low cross.
From his second ball in the Whites wingback had keeper Nathan Bishop backpedalling to claw the ball away one-handed.
Southend's Elvis Bwomono was then rightly booked for a late challenge on Inih Effiong as he looked to lead a swift counter and, as the action continued unabated, Stephen McLaughlin fired over after a decent move by the visitors.
Southend's McLaughlin became the second man booked in a matter of minutes after catching Michael Woods late and the game was still only 19 minutes old when Isaac Hutchinson drew a low diving save from Mersin.
The game's third booking went to Dover's Taylor after he pulled down Bwomono. and that was followed by two good chances in quick succession for Reason.
The first came after Effiong had done well to knock down Scott Doe's deep diagonal cross into the path of Reason, but under pressure, he snatched at his shot which sailed well over.
The home midfielder was better with his aim moments later when his low drive from 22 yards was well turned aside by keeper Bishop diving to his right.
Dover went even closer to a breakthrough on 35 minutes when Bishop failed to claim Munns' corner under pressure from Paul Rooney and Southend striker Tom Hopper was forced to clear off his line.
Mersin then went down to his left to save Ethan Hamilton's low drive but that was the last chance of the half and Whites would have gone in at half-time much encouraged.
That was reflected in the way they began the second half with Effiong doing well to create a shooting chance only to send his angled drive wide of the far post.
Southend lost defender Shaughnessy to injury just before the hour and moments later Whites had a great opportunity when a corner dropped to Reason at the far post but he blazed over.
The midfielder immediately put his head in his hands illustrating how good a chance he felt it was.
Southend optimistically appealed for a penalty when McLaughlin's 64th minute cross struck Oscar Gobern at close quarters but referee David Rock waved their claims away.
You sensed Whites knew the tie was there for the taking with Effiong, Steven Rigg and Munns all seeing efforts either blocked or deflected before Rooney headed over after beating keeper Bishop to a corner.
Rooney then picked up a booking for a blatant block and both teams then made substitutions as the game entered the final 20 minutes.
Nassim L'Ghoul replaced Gobern while for Southend Emile Acquah and Simon Cox came on for McLaughlin and Brandon Goodship.
L'Ghoul immediately went close with a glancing header which forced Bishop to save and Southend swiftly broke down the other end with Bwomono's cross going right across the face of the home goal.
Whites threw on loan signing Sotiriou for his first taste of the action since signing from Orient and what an impact he made.
He had only been on the field three minutes when he got the ball out wide, cut in and rifled an unstoppable shot across Bishop and into the far corner.
L'Ghoul then made a terrific block at the other end and in a frenetic finish Reason almost made it 2-0 when his clever lob clipped the top of the cross bar.
Cox should have done better for Southend than shoot straight at Mersin but Dover saw out the five minutes of added time to clinch a famous win.
Dover: Mersin, Simpson, Taylor, Doe, Rooney, Woods, Munns (Cumberbatch 86mins),Reason, Gobern (L'Ghoul 73mins), Effiong, Rigg (Sotirou 81mins); Subs: Worgan, Bedford, Jeffrey, Ratti.
Southend: Bishop, Lennon, Dieng, Shaughnessy (Kiernan 59mins), Bwomono, Ralph, Hamilton, Hutchinson, McLaughlin (Aquah 73mins), Hopper, Goodship (Cox 73mins); Subs: Oxley, Demetriou, Milligan, Taylor,Kiernan
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