Phil Smith's verdict: The major changes unfolding in the League One promotion race underline why this Sunderland win was so key

It has been a division where for much of the campaign, the margin for error has been considerable.

Teams have been able to endure a wretched run of form but come out of it with their promotion hopes just about unscathed.

Shortly before the turn of the year, Tom Flanagan candidly admitted that the Black Cats were probably fortunate that their midwinter run had not left them further back from the pack.

It’s been said often that there has not appeared to be a side with the quality and consistency of either Luton or Barnsley, and that automatic promotion may well be achieved this year with a relatively unimpressive points total.

A glance at the table still underlines that.

No side is tracking at two points-per-game and there aren’t too many even particularly close.

This time last year, Luton had already moved well ahead of that mark. Barnsley were right on it, while both Sunderland and Portsmouth were right on the edge.

Nevertheless, the standard at the top is going up by the week.

It has been a remarkable turnaround for the Black Cats since that acrimonious Boxing Day draw with Bolton Wanderers, their form in that period is firmly that of automatic promotion contenders.

The defeat to Portsmouth was bitterly disappointing, but otherwise they have been a resilient unit and their defensive record has been exceptional.

They have conceded just once in four games at the Stadium of Light in that time, and only five overall, keeping five clean sheets in their last six.

Only Rotherham United have bettered their points haul in that period but it is notable that they are merely one of a number of teams beginning to make a serious play in the push for the top two.

Paul Warne’s side have been exceptional, while Portsmouth and Coventry City have also taken more than two points-per-game in that timeframe. Crucially, the quality of their performances over a period of time suggest that it is form that they have a solid chance of sustaining.

Portsmouth, in particular, have looked like an elite League One side for some time. Their early-season results were curious, Kenny Jackett’s side struggling for points even when the data was suggesting that they were one of the best sides in the division.

Though Peterborough’s points haul in that time is less impressive, it is worth pointing out that they have won five in a row, including wins over Rotherham, Oxford, Ipswich and Wycombe.

After a mid-season malaise to rival Sunderland’s, Darren Ferguson has shuffled his pack and found an attacking formula that teams are struggling to live with.

The departure of Marcus Maddison appears have to been liberating, Sammie Szmodics thriving and forming a superb attacking trident with Siriki Dembele and the outstanding Ivan Toney.

On Saturday they made something of a statement, 2-0 up against Oxford United when they went down to ten. They went on to score two more.

The division remains wide open, and any side in the top ten will justifiably feel they still have a chance of achieving automatic promotion.

The difference now is that it no longer feels as if the teams that go up will stumble over the line.

It’s wide open, but the standards are getting higher, and just serves to underline why Chris Maguire’s strike could prove to be one of the most important of the season.

The reaction to the defeat at Fratton Park had been measured, with an understanding and acceptance that it was one poor result following a string of big wins.

There remained nevertheless an understandable concern that this was a side that struggled to beat the teams around them, and that only when that changed could they be considered genuine contenders for the top.

The first half did not bode well.

It felt as if Sunderland were letting another opportunity pass them by, Ipswich by far the more composed and fluent side.

Both sides played with five at the back but Ipswich’s system is slightly different in that they play with another central midfielder and a second orthodox striker, rather than with the inverted wingers.

With Will Keane dropping deep to effectively form a midfield diamond, Sunderland couldn’t build any spells of possession.

They were outplayed and fortunate that Ispwich’s poor form means there is perhaps a lack of composure and confidence in the final third.

It said everything that Denver Hume had barely had a touch in Ipswich’s half. When Sunderland are good, particularly at home, he is a constant attacking outlet.

That was firmly the case in the second half, Sunderland almost entirely dominant and more than worthy of the points.

George Dobson and Max Power stepped up in midfield, disrupting the opposition and moving the ball with more speed and precision.

Parkinson’s change proved key.

Duncan Watmore looked set to come on when the Black Cats boss had second thoughts, instead sending on Kyle Lafferty for a touch extra presence in the final third.

It paid immediate dividends.

Some games just have that feel of being a little more important, and the eruption as Maguire fired the ball into the bottom corner told you that this one of those.

This has always had the feel of a defining month for the Black Cats.

It was not an emphatic start, but it was a truly crucial result.