Just three days after the 4-0 win at the ABAX Stadium, a brilliant first half free-kick from Tony McMahon and a second half goal credited to James Hanson proved enough for Parkinson's men to defeat Southend and make it back-to-back victories.
City's second goal came via a McMahon corner delivery which was headed against the crossbar by Hanson before the ball was bundled home. With Steven Davies lurking nearby, the ball appeared to possibly bounce off Southend goalkeeper Daniel Bentley last before going over the line but Hanson was still initially credited with the goal.
Tuesday's game at the Coral Windows Stadium was a game in hand for City on other teams in the division.
Helped also by losses for Millwall and Sheffield United on the same night, the Southend win for Parkinson's side moved them to within three points of the League 1 Play-Off places having played a game less than sixth-placed Millwall.
Parkinson said: "It was important that we built on Saturday's (vs Peterborough) performance.
"We knew Southend would come and make it difficult. They came with a 4-5-1 formation and flooded that midfield area so the first goal was always going to be important.
"It was a great free-kick from Tony (McMahon) to give us the lead, and I felt we controlled the game thereafter for the most part.
"Those moments of quality in any game are always so crucial.
"There was a period at the start of the second half where we couldn't really get any play in their half but the second goal has given us that vital cushion.
"It was a great delivery by Tony from the corner and James (Hanson) and Davo (Steven Davies) have gone in there with real intent. I think James will end up getting the goal but the main thing is that it has gone in.
"Apart from Saturday's defeat at Scunthorpe, Southend have been on a good run lately so we knew it would be tough but we were resolute.
"There was a good feeling around the dressing room before the game. It was important that we got the three points tonight with it being a game in hand for us, and I could feel the lads were really focused on the job in hand tonight (Tuesday)."
Following the birth of Rory McArdle's first child, Nathan Clarke was brought back into the side as the only change from the team that began the Peterborough fixture.
Parkinson continued: "Nathan was brilliant for us.
"Every time he has played recently he has been faultless really. Even when he has not been in the team, his character in and around the training ground has been fantastic.
"He has worked with the young defenders in the team, he has been a great example to them. When he has played, he has been tremendous, you can't ask any more of him.
"He is a proper leader and he certainly adds something to the team when he is in it."