A LATE winner from Aribim Pepple saw Southend United win 1-0 to knock Eastleigh out of the FA Cup in fourth-round qualifying.
The substitute beat Joe McDonnell at the near post in the third of five additional minutes as the tie looked certain for a replay.
Tyrese Shade and Paul McCallum had chances for the hosts but were left ruing their missed efforts.
Davis made two changes from the side that lost 3-1 to Forest Green last weekend, introducing Lloyd Humphries and Luis Fernandez.
The changes saw top goalscorer Paul McCallum drop to the bench - as did defender Richard Brindley.
Eastleigh were 2-0 losers when these two sides met at Roots Hall Stadium in National League action earlier this season.
The retired goalkeeper had hoped Saturday's tie would see the Spitfires return to winning ways after three games without victory.
After a back-and-forth start, Eastleigh's first moment of danger came as a result of an inviting long ball from Fernandez.
The defender looked to have found Scott Quigley in behind but Colin Andeng-Ndi raced out to pinch the ball.
The hosts saw more joy from playing the ball in behind as Chris Maguire was taken out just as he played Shade through.
Referee James Durkin waved on the play, opting for advantage, but Shade was unable to make the most of his chance, which was saved by Andeng-Ndi.
Eastleigh players were incensed that Southend were not reduced to 10 men and showed their anger to the referee as a devastated Shade held his head in his hands.
Davis was forced into an early change just before the break when Welsh midfielder Humphries went down for the second time in the first half. He opted to go more attacking, introducing McCallum.
Eastleigh remained a threat after the break and came close to scoring soon after the restart when captain Jake Taylor fired over from the edge of the box.
The Shrimpers slowly started to grow as the second half progressed but were denied a chance when Joe McDonnell went to ground on the hour mark.
Josh Walker had beaten Eastleigh's goalkeeper to the ball but he stayed down when it spun free and into the direction of an away player.
McCallum, an aerial threat throughout his substitute cameo, came the closest to a second-half goal for Eastleigh when he headed just over from Shade's cross.
Former Scotland international Maguire tried a trademark long-range effort on 75 minutes before Davis turned to summer signing Jai Semenyo, brother of Cherries forward Antonie, in search of a winner.
Southend had a tame penalty shout turned away in the dying moments as the game looked to be heading for a replay.
But it didn't matter as Pepple, on from the bench, squeezed in at McDonnell's near post to send the Shrimpers through.
Eastleigh: McDonnell, Vokins, Humphries (McCallum, 39'), Fernandez, Francillette, Maguire (Semenyo, 80'), Taylor, Shade, Waruih, Quigley, Maher.
Unused subs: Scott, Brindley, Panter, Boutin, Semenyo, McDonald.
Southend United: Ndi, Scott-Morriss, Ralph, Crowther, Husin, Bonne (Pepple, 66'), Walker (Bridge, 80'), Gubbins, Taylor, Morton, Coker (Moncur, 66').
Unused subs: Brown, Wind, Wood, Appiah-Forson.
Referee: James Durkin.
Attendance: 1,659.
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