Wes Burns’s 27th-minute goal has given Town a 1-0 half-time lead over Huddersfield at Portman Road at half-time, while third-placed Leeds are 2-1 behind to Southampton.
Town boss Kieran McKenna made three changes from the team which won 2-1 at Coventry on Tuesday.
Luke Woolfenden returns at the heart of the defence for his hometown club with George Edmundson dropping back to the bench.
Conor Chaplin came into side in the central role behind striker George Hirst with Nathan Broadhead and Kieffer Moore also among the subs having started Tuesday’s match.
All-but-relegated Huddersfield made four changes from the team which drew 1-1 at home to Birmingham last week with keeper Chris Maxwell, Tom Edwards, Ben Jackson and Ben Wiles all starting.
Young right-back Neo Eccleston was on the bench for the first time along with two keepers, usual first-choice Lee Nicholls and youngster Giosue Bellagambi.
The Blues, whose had been greeted by a huge crowd of fans assembled by Blue Action as they arrived at the ground, got the game under way, unusually attacking the Sir Bobby Robson Stand.
Town started confidently and Axel Tuanzebe struck the game’s first shot in the eighth minute, the ball deflecting wide for the first of two corners.
On 11, Burns crossed low from the right and Omari Hutchinson appeared to upended as it came over, however, Premier League referee Simon Hooper waved away the protests.
From the corner, Conor Chaplin looped the ball back in and Hirst nodded across the face and wide.
In the 13th minute, with the Blues dominant and the home fans getting firmly behind them, Hutchinson tried a clever backheel into the path of Burns inside the box but the Wales international failed to read it.
Three minutes later, Chaplin turned his man 25 yards out before hitting a low shot which flew just wide of Maxwell’s left post.
On 18, after Hutchinson had just failed to keep the ball in on the byline on the left, a murmur around the ground gradually grew into a roar as news of Southampton going in front at Leeds filtered through.
Two minutes later, the Blues broke following a Huddersfield attack but Burns shot over from just outside the box having been teed-up by Hutchinson. News that Leeds had quickly equalised similarly worked its way around the Town support.
Town continued to create chances. In the 23rd minute, Hutchinson stood up a cross from the left, Burns nodded back across goal but Chaplin headed well over, much to his frustration.
Two minutes later, the Blues missed an even better chance. Chaplin played in Burns with a great pass and the Welshman slipped it past the advancing Maxwell but wide of the keeper’s right post. It was the best opening up to that point.
But Burns and the Town support didn’t have to wait too much longer for their side to go in front.
Hutchinson won the ball off a dawdling defender on the left and fed Hirst, who moved it on to Chaplin, who swept it wide to Burns on the right of the box and the Wales international slammed a shot between Maxwell and his left post to take the roof of Portman Road.
Burns’s sixth goal of the season, which had been coming, was effectively worth two with Huddersfield needing to win to upset Town’s afternoon.
On the half-hour, three minutes after going behind, the visitors made what looked to be a tactical change, Alex Matos replacing Jack Rudoni.
On 33, Town were denied what looked a very solid penalty claim. Chaplin was sent away on the right of the box and was about to cut across to the unmarked Hirst when he was felled.
Referee Hooper waved away the protests and then almost immediately gave another decision against the Blues when Burns appeared to be tripped, before giving a subsequent free-kick to Chaplin, who angrily made a point regarding the penalty claim and was spoken to at length by the official.
In the 40th minute, news of Southampton’s second goal at Leeds having been warmly received around the stadium, Hutchinson turned and skipped away from his man before breaking towards the area but scuffed his low shot wide.
A minute later, Morsy slammed a powerful strike which Maxwell snaffled at the second attempt. It had continued to be all Town with the only surprise they hadn’t extended their lead.
Moments after the fourth official indicated an additional four minutes, a long throw was cleared to Massimo Luongo, who hit a first-time strike which flew over the bar.
The whistle was greeted by applause, the half having gone as well as Town could have hoped aside from adding to their one-goal lead. But with Leeds 2-1 behind at half-time, the Blues had a four-goal cushion across the two matches going in at the break.
Town had been in control and comfortable all half and had created enough chances to have been 5-0 ahead, as they were in the similar game at home to Exeter, which confirmed promotion from League One a year ago.
A steady second half and the Blues will be back in the Premier League for the first time in 22 years.
Town: Hladky, Tuanzebe, Woolfenden, Burgess, Davis, Morsy (c), Luongo, Burns, Chaplin, Hutchinson, Hirst. Subs: Walton, Clarke, Edmundson, Travis, Taylor, Jackson, Sarmiento, Broadhead, Moore.
Huddersfield: Maxwell, Pearson, Helik (c), Rudoni, Edwards, Kasumu, Turton, Wiles, Ward, Jackson, Healey. Subs: Nicholls, Bellagambi, Radulovic, Koroma, Spencer, Matos, Jones, Iorpenda, Eccleston. Referee: Simon Hooper (Wiltshire).