Rosenior’s side took the lead through Neto’s superb first half strike before the Portugal forward netted again after the break.
Estevao Willian scored Chelsea’s third and Neto completed his treble to wrap up the fourth round rout at the MKM Stadium.
It was an emotional evening for Blues boss Rosenior as he faced the club that ruthlessly severed their long relationship with him in 2024.
Rosenior supported Hull as a child alongside his season-ticket holding grandmother, played for the club across five years and managed them for two seasons.
He was sacked after narrowly failing to reach the Championship play-offs amid criticism of his team’s conservative tactics.
Despite the painful end to his time at Hull, the 41-year-old said it was an “amazing thing” to return to Humberside and he took full advantage of the chance to show his old club what they missed out on.
Rosenior has made an impressive start at Chelsea since arriving from Strasbourg to replace Enzo Maresca in January, winning eight out of his first 11 matches in all competitions.
He made seven changes, with Cole Palmer, Enzo Fernandez and Joao Pedro among those to miss out, but Chelsea were still too strong for the Championship promotion chasers.
Estevao wasted a glorious early chance, dancing around Hull keeper Dillon Phillips only to lose his composure and shoot high over the empty net.
Liam Delap spent the 2023-24 season playing under Rosenior on loan at Hull.
Delap was denied a goal on his return in bizarre fashion as Phillips miscued a clearance that hit the Chelsea striker and deflected off the bar before he failed to convert the rebound.
Chelsea dominated possession to such an extent that it was little surprise when they finally made the breakthrough in the 40th minute.
After missing much easier chances, they produced an eye-catching goal to take the lead as Delap teed up Neto, who whipped a superb finish into the corner from 20 yards.
Andrey Santos’ towering header was pushed over by Phillips after the interval and, from the resulting corner, Chelsea doubled their lead in the 51st minute.
Neto’s inswinger caught Phillips flat-footed at the near post, bouncing through his legs without a touch from either team.
Chelsea had blown a two-goal advantage in their 2-2 draw with Leeds in the Premier League on Tuesday.
But there was no chance of a repeat and Estevao grabbed their third with a composed finish from 12 yards in the 59th minute.
Neto made it four in the 71st minute, caressing a low finish past Phillips from Delap’s lay-off.
Wrexham beat fellow Championship side Ipswich 1-0 in Friday’s other fourth round tie.
The Welsh club, owned by Hollywood actors Ryan Reynolds and Rob Mac, are into the last 16 for the first time since 1996-97. (AFP)
