After an evenly fought opening period at The Den, Fredericks’ cross-cum-shot somehow found its way into the top corner to give Millwall a 39th minute lead.
Lee Martin missed a golden opportunity to double the advantage in the second half but wasn’t made to pay for his poor finish as Holloway’s side saw out the game.
The win is Millwall’s first since December 7 and only their second in 10 games, but fans will hope it’s a sign of things to come under new management.
Holloway was welcomed with emphatic home applause as he emerged from the tunnel for what was billed as the start of a new era. Both teams were struggling for form heading into the game and it showed in was a scrappy start.
Liam Trotter carved out the first attempt in the 17th minute, curling the ball just wide from 20 yards.
Both teams found it hard to settle but it was Millwall who were the more attacking of the two. Despite all of Millwall’s decent play, though, it was Ipswich’s Daryl Murphy who was the first player to seriously test a keeper.
Latching onto David McGoldrick’s tidy flick, Murphy fired a low shot at David Forde but the home keeper saved well.
Ipswich soon grew into the game as they began to enjoy more and more possession.
However, just as it looked as if Millwall would do well to enter half-time level, a freak goal from Fredericks sparked wild celebrations from the home fans.
After good work down the right from on-loan Spurs defender, Fredericks’ over-hit cross evaded everyone to nestle into the top corner.
And despite seeing keeper Forde forced off through injury late in the half, Holloway would have been very pleased with his team’s efforts in the opening 45 minutes.
Mick McCarthy would have felt his players were in need of a talking to during the break but whatever he said worked as they came out fighting in the second half.
Tommy Smith had a header cleared off the line by Martin and Murphy saw an effort on goal thwarted by a late Danny Shittu tackle as Ipswich looked to find an equaliser.
The game continued at a frantic pace, with both teams enjoying a number of chances.
Millwall nearly doubled their lead in the 63rd-minute when the ball fell to Scott Malone just outside the six-yard box but the defender could only volley wide.
Holloway’s side began to find openings and should have made it 2-0 in the 69th-minute after good work from Martin.
The former Ipswich man did well to beat two defenders in the box but could only fire over from six yards to the disbelief of the home fans.
Ipswich were far from finished, though, and substitute David Taylor missed a golden opportunity with just five minutes left.
After a quick break from the visitors, Taylor found space in the box but saw his shot well saved by replacement keeper Stephen Bywater before Malone cleared the danger. Ipswich continued to search for the equaliser but it never came as Millwall recorded a very welcome clean sheet to take all three points.
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Millwall: Forde (Bywater 44), Fredericks, Shittu, Lowry, Malone, Trotter (Abdou 69), Bailey (Wright 61), Martin, Keogh, Morison, McDonald. Subs not used: Feeney, Woolford, Beevers, Marquis.