Elliot, who endured virtually a full season out following a back operation, finally made a start to his West Ham career against the Shrimpers just after returning from Peterborough on loan.
What made his display all the more remarkable was the fact that he was in a side that had not played - or even practised - together before.
"There were three debuts with myself, James Walker and Mark Noble, while Trent McClenahan made his home debut, so for a team that hasn't really done any team work before the game I thought we did really well to get into the next round.
"I came back from Peterborough on Monday and luckily got my clearance - I had just one day back training and it was just short and sharp stuff.
"Then the gaffer picked the team and told us to go out there and win the game no matter what - which is what we did.
"I was a bit nervous but once I got over the first touches and passes I think I settled in well, so I was happy with my game."
There was an anxious moment when, in the second half and with Southend pressing, he slipped to allow Southend's right winger to race in and cut the ball back.
Fortunately Tomas Repka was on hand to save the day.
"There were a few things I could have done better and when I slipped they got in - but Tomas did a bit of 'Brazilian' play to intercept," smiles Elliot.
"I was lucky he got me out of trouble there and he did well; I was just praying they didn't score, and it would have upset me if they did, because I thought I played quite well.
"It would have put them back in the game, obviously, but luckily it didn't happen."
Elliot didn't even have time to consult his Czech phrasebook before the game and he jokes:
"I didn't understand some of the things he said.
"But he helped me, as did Rufus on the left; it was good to have those players around me."
He is philosophical about the fact that he could have had his chance a year ago had he not needed an operation.
"It could have happened before, but that is life; I got injured, I have come back, and with a few injuries I had to take my chance.
"I have waited a long time; now I have done it, and Alan said 'well done' after the game - but the main thing is the win.
"They could have scored, but they didn't, and that is three clean sheets in five games.
"I was bit tired after the game but I slept well and my back problems are completely over."
Brother Darren plays for Millwall, just to add a bit of spice to the sibling rivalry, but for once it was Elliot in the spotlight.
"He sent me a text to say 'good luck' and I had my other brother, girlfriend and family watching - and there was good support from the crowd, which helped, as did the players.
"Headlines don't bother me - as long as we win, that is the main thing."
Of the game overall, he says:
"I think in the first half we had the better of them, and obviously we were a goal up, so I think they realised they had to come to us a bit more in the second half.
"We found it a bit hard to keep the ball at times and they put more pressure on the defence so it was important we kept a good line and defended well."
Elliot is pleased to be back on home territory after a month with the Posh, and he explains:
"I went there to play games and I got them - but in the reserves.
"I was in the squad once and decided to come back on Monday and give it a try here.
"They wanted me to stay another month but I didn't really want to because I wanted to play and needed to.
"I got given a chance so I was very happy about that - but there are players coming back this weekend so we will see."