Derby days do not get much sweeter for Norwich City. Their hex over Ipswich Town extended to 15 years and the consequences of this feisty, fully merited win may be greater still. For one thing, it puts a severe dent in their rivals’ hopes of automatic promotion, which had looked irresistible at the outset; for another, it tightens their own stranglehold on sixth place and infuses their playoff challenge with potentially decisive momentum. Whisper it quietly, but this may only have been an appetiser: with this result, the odds on a reunion in the playoffs next month have surely shortened dramatically.

Marcelino Núñez was the hero for David Wagner’s team, beating Vaclav Hladky with a 39th-minute free-kick during a spell of concerted Norwich pressure. It said everything for their display that they restricted the league leaders, usually so swashbuckling, to scraps and there was no scope on this occasion for Kieran McKenna to mastermind one of Ipswich’s trademark late comebacks.

A fast, frenetic start brought positive intentions but few openings. Norwich, smart and snappy, showed plenty of appetite for the challenge and little intention to allow Ipswich to develop any rhythm. The tackles flew in and it was a welcome surprise that the referee, Matthew Donohue, surely recognising the gravity of the occasion, opted not to make use of his yellow card during the opening half-hour.

That finally changed when Axel Tuanzebe, the Ipswich centre-back, gave chase to Josh Sargent after Ashley Barnes had sent Norwich’s top scorer away down the inside right channel. Tuanzebe recovered sufficiently to offer a challenge and, as replays suggested, get a toe on the ball; Donohue saw a foul and, from that point, the remaining decision was whether to keep him on the field. A booking was deemed sufficient and, from plum on the 18-yard line, Núñez squandered the free-kick.

It was among a succession of set pieces Norwich earned in dangerous areas during a spell that saw Ipswich struggle to clear their lines. Núñez is a ball striker of some quality and the visitors soon discovered that offering him multiple chances to showcase the fact was foolhardy. When Sam Morsy conceded a needless foul 25 yards out Núñez struck a swerving, wobbling effort that Hladky, diving to his left, could only push onto his left post and in.

On balance Norwich merited the lead. McKenna had indulged in what by his standards was a rare piece of pre-match kidology by casting doubt on the participation of the totemic centre-forward Kieffer Moore, who sustained a minor back problem in the riotous win over Southampton. It was little surprise to see Moore wheeled out for the occasion but he was not given a sniff before half-time. Ipswich were smothered, unable to create and only causing genuine flutters when Omari Hutchinson went down in the box under Borja Sainz’s challenge soon after Núñez’s flourish.

It was not quite enough for a penalty and Ipswich would require a different way back. They were allowed the lion’s share of possession after the restart but still struggled to make any headway, their hearts firmly in mouths when Sainz fluffed an attempt to lob Hladky.

When Morsy, below par and scrambling to atone for losing possession in midfield, bundled Sargent over in the ‘D’ there were howls of incredulity from the stands. He had been lucky and Ipswich needed to improve markedly. McKenna, who has few parallels in his use of substitutes, introduced Harry Clarke and Jeremy Sarmiento in the hope of injecting some life into the flattest of displays.

Hutchinson managed their first shot on target in the 67th minute but Norwich, simply sharper, threatened again when the breaking Sargent forced a fumbled save from Hladky. Then Sainz lofted over after fine work from Sargent and, by now, Wagner’s side could have been home and dry.

Finally Ipswich wrought an opening, Conor Chaplin firing Leif Davis’s centre over in his last act before being replaced. One of their new arrivals, Ali Al-Hamadi, was sent behind the defence but an underworked Angus Gunn met the moment and blocked heroically. The Carrow Road roar at full-time was deafening and perhaps these bitter foes will soon be doing it all again.