The Spireites' Tuesday win sets up an almighty match at the Abax Stadium between two teams with sights fixed on the play-offs.
The sides are separated by a margin of just one place and two points, the Spireites also holding a game in hand, and both teams come into the match in good recent form.
Midfielder Sam Morsy hass now completed his two-game suspension and is in contention to go straight back into the starting 11 for the match.
The returning Drew Talbot reported stiffness after his first 90-minute Spireites run out on Tuesday, but is expected to keep his place in the unfamiliar left back for the match. Having made eight consecutive starts during his loan spell at Plymouth Argyle Talbot is progressing well from his long-term groin injury.
Like the Spireites, United are generally free of injury concerns and Jack Baldwon and Jermaine Anderson are the only two players on the treatment table - though midfielder Marcus Maddison remains suspended and will miss the match.
The midweek win over Gillingham boosted both the Spirieites' confidence and league position and the side have now won three of their last four games to sit eight in the League One table.
Peterborough on the other hand suffered a 2-0 defeat at in-form Preston North End midweek, the defeat coming after four straight league wins for the Posh under caretaker-manager Dave Robertson.
Robertson took over from Darren Ferguson in February and has turned the Posh's form around and spearheaded the side's current play-off push.
In the reverse fixture this season, the Spireites ran out Boxing Day victors, steaming into a three-goal lead before two second-half strikes tightened the scoreline, Chesterfield holding steady to earn a 3-2 win.
From the Dugout
Speaking to Spireites Player ahead of the game, manager Paul Cook spoke about the mood amongst his squad after the midweek victory.
"The lads are buoyant," said Cook. "The lads are in good form. The sun's coming out now and hopefully the pitches will pick up and get a little bit better. We've got a lot to play for and I think our supporters will be really pleased with that.
"Tuesday was important, we couldn't lose that, we'd have given ourselves a little bit too much to do. If we don't win tomorrow we'll have nine games to go and we can still get in the play-offs - winning tomorrow puts us in a great position.
"We've got a few away games to go, I know we'll take good support, I know they'll get behind us and a win wouldn't half give us a big boost."
With the two sides familiar with each other after recent Wembley and League One encounters, Cook feels he has an idea of how the Posh will line up against his team.
"They seem to be playing with 4-4-2 with Washington and James up front," said Cook. "They've had some great results, unfortunately they've lost at Preston on Tuesday, but there were four straight wins before that.
"They're doing really well and every game's tough. We went to Rochdale and Scunthorpe and lost, then we've gone down to MK Dons and won so you can't look at any game and say you'll be okay.
"They've got good players, we know each other well now after Wembley. We've got a lot of documentation on Peterborough and them on us, we're just looking forward to the game."
For those unable to get to London Road on Saturday there are a range of ways to follow the match. Supporters can listen to live full match commentary on Spireites Player, follow minute-by-minute coverage on Twitter and score updates on Facebook.
Furthermore, fans can try out the Spireites Player service for free for seven days, and take advantage of the offer to listen to tomorrow's Posh clash. Just follow this link.