Steve Bruce's side, relegated from the Premier League last season, retained first place on goal difference ahead of Brighton thanks to goals from Mohamed Diame, Sam Clucas and Tom Huddlestone.
Diame opened the scoring against fourth placed Middlesbrough just before the interval and second-half strikes from Clucas and Huddlestone ensured a fifth successive league win for the Tigers.
Brighton kept the pressure on Hull as Chris Hughton's team ended a run of three consecutive draws with a 2-1 win against Milton Keynes Dons at the Amex Stadium.
Solly March and Jamie Murphy gave Brighton a flying start with goals in the opening 20 minutes and although the struggling Dons quickly responded through Nicky Maynard, they couldn't find an equaliser.
Third placed Burnley, who started the day level on points with Hull and Brighton, could only draw 0-0 at Wolves to slip two points adrift of the automatic promotion spots.
Birmingham took advantage of Derby's 1-0 defeat at local rivals Nottingham Forest on Friday to move to within two points of the fifth-placed Rams with a 5-2 drubbing of 10-man Fulham at Craven Cottage.
Stephen Gleeson, Paul Caddis and Jon Toral put Birmingham 3-0 ahead inside 31 minutes and, after Fulham had lost James Husband to a 49th-minute red card, Clayton Donaldson and Viv Soloman-Otabor added late goals for the visitors.
Fulham's goals came from Alex Kacaniklic and Ross McCormack when the hosts were 3-0 and 4-1 down.
Daryl Murphy bagged a hat-trick in Ipswich's 5-2 victory at bottom of the table Rotherham.
Brett Pitman and Jonathan Douglas had earlier put Ipswich 2-0 up, with Rotherham briefly threatening an unlikely comeback with goals from Brandon Barker and Matt Derbyshire just before the hour.
Cardiff moved above Reading into seventh with a 2-0 win over the Royals, while struggling Charlton celebrated their first victory since August after beating in-form Sheffield Wednesday 3-1.
Leeds recorded back-to-back wins for the first time this season after beating Yorkshire rivals Huddersfield 3-0.
Mirco Antenucci and Chris Wood both netted in first-half stoppage time before Alex Mowatt crashed home a third after the break.
Blackburn and Brentford shared a 1-1 draw at Ewood Park, Tom Lawrence cancelling out Lasse Vibe's goal for the visitors, while Preston recorded a sixth successive clean sheet in drawing 0-0 at QPR.
Bolton had to settle for a 0-0 draw against relegation rivals Bristol City after Shola Ameobi's second-half penalty was saved by City keeper Frank Fielding.