Conor Shaughnessy and Colby Bishop claimed quick-fire goals as Portsmouth boosted their Sky Bet Championship survival hopes by denting Ipswich's automatic promotion push with a 2-0 win at Fratton Park.
Defender Shaughnessy set Pompey on course to move four points clear of the relegation zone by heading home Adrian Segecic's corner in the 42nd minute.
Striker Bishop doubled the lead just two minutes later, slotting a loose ball in the bottom right corner from close range to stun the Tractor Boys and spark wild celebrations among home supporters.
Second-placed Ipswich remain two points above third-placed Millwall with a game in hand after slipping to a surprise first defeat in 10 outings.
Following the euphoria of Saturday's 2-0 derby victory at Norwich, the Ipswich faded from a bright start and barely tested home goalkeeper Nicolas Schmid.
This fixture went ahead at the third time of asking following postponements in January and February due to a frozen pitch and a waterlogged pitch respectively.
Ipswich travelled to the south coast buoyed by regaining second spot thanks to victory at Carrow Road, while Pompey had kept themselves out of the bottom three courtesy of a last-gasp 1-0 win away to promotion-chasing Middlesbrough.
Town striker George Hirst saw an early opportunity blocked behind for a corner before Portsmouth left-back Jordan Williams curled wide at the other end during an intense opening lacking clear chances.
Pompey winger Millenic Alli almost opened the scoring in spectacular style when his dipping effort from distance was tipped over by Ipswich goalkeeper Christian Walton in the 27th minute.
Ipswich boss Kieran McKenna has been linked with the Bournemouth job following news earlier on Tuesday that Andoni Iraola will leave the role in the summer.
His high-flying side went into half-time two goals down following a costly three-minute spell.
Centre-back Shaughnessy made the breakthrough, escaping the attentions of Hirst to nod in Segecic's inswinging delivery from the right.
Home fans had barely finished celebrating when Bishop swept into the bottom right corner after two efforts from John Swift were blocked following Andre Dozzell's cross from the left.
Chants of "we are staying up" rang around the ground as Ipswich's players gathered for an impromptu on-field team talk.
Portsmouth manager John Mousinho had described this game as a "bit of a free hit" for his team.
Moments after Town boss McKenna introduced attacking duo Jaden Philogene and Anis Mehmeti as part of a triple change, Pompey could have gone further ahead but Segecic directed his diving header wide of the left post following Alli's delivery.
Ipswich took until the 67th minute to register an attempt on target. Marcelino Nunez's effort from range was comfortably caught by Schmid, while Mehmeti later dragged wide.
Schmid saved well from Philogene in added time but the visitors could have few complaints about the result as their quest to secure an immediate return to the Premier League suffered a setback.
Portsmouth's John Mousinho:
"In the moment it feels like the best performance since I've been here, and there's been some good ones.
"(It's) definitely the best performance of the season and with everything taken into account - circumstances, where we've been over the past few weeks - I think all of that is justified.
"The mentality off the back of the win on Saturday is something we haven't had for the majority of the season.
"Whenever we've won games, we've never followed it up.
"We did it once, Charlton to Millwall (in February) but there have been a lot of false dawns where we've won one game, turned a corner, played brilliantly well and the next game it's not quite been there."
Ipswich's Kieran McKenna:
"If you concede the first goal from a set-play at this stadium with the atmosphere as it was tonight it's always going to be tough, and to do it just before half-time was a blow.
"We're really disappointed with that goal and then to concede probably a minute later, if you take the celebrations out of it, that killed the game for us.
"That's really the key couple of minutes in the game. Before that, we would have liked to play a bit better in terms of creating chances but it was always going to be a tough night.
"If we get to half-time at 0-0 it's probably been a pretty steady first half and we're in a position to push on.
"But you let the game go like that in a couple of minutes before half-time, a really difficult game becomes not impossible but much, much, much more challenging.
"You would have to do fantastically well in that second half to turn it around, and we didn't manage to do that."
