Lukaku publically questioned the club's ambition in the days preceding Saturday's contest to cast doubt over his Everton future, but the Belgian added the gloss to a convincing victory as he moved top of the league's scoring charts with a late double at Goodison Park.
Dominic Calvert-Lewin squandered a terrific chance in the reverse fixture in December, but the youngster made no mistake on this occasion as he nudged in Tom Davies' cross to give Everton the lead early on.
Marco Silva's side responded well to going behind, but any hopes of a Hull comeback were all-but ended when Tom Huddlestone was dismissed - harshly so - for a lunge on Idrissa Gueye midway through the second half.
Valencia secured the points just over a minute after coming on, with Lukaku adding a quickfire double. Hull remain planted in the relegation zone, while Everton - who face Liverpool after the international break - move level on points with fifth-placed Arsenal.
Despite Lukaku's reported refusal to sign a new contract, Everton fans showed no hesitation in getting behind the striker as the teams were announced in the pre-match build-up.
But for all of the attention on the Belgian, it was Lukaku's strike partner Calvert-Lewin who opened the scoring after nine minutes.
Ross Barkley and Davies combined brilliantly to set-up the 20-year-old, who duly tucked home to open his Premier League account.
Calvert-Lewin went close to a second before Lukaku looked to have responded perfectly to his critics when he found the net, only for a late offside flag to deny the former Chelsea man his 20th league goal of the season.
Gareth Barry replaced the injured Morgan Schneiderlin on the half-hour mark, and the veteran nearly made an immediate impact with a cross into Ashley Williams, who headed straight at Eldin Jakupovic.
Hull looked bright after the restart, with Everton lacking the zip and guile that was present in the opening stages, though Lukaku went close with a rasping strike.
Lukaku, desperate to reinforce his comments with a goal worthy of a world-class talent, forced Jakupovic into a fine save soon after, while Andy Robertson should have done better with a close-range volley at the other end.
But as Hull looked to be building a head of steam, they were reduced to 10 men - Huddlestone receiving a straight red card after diving in on Gueye.
Everton soon made their numerical advantage pay - Lukaku teeing-up Valencia with a delightful flick - the West Ham-loanee proceeding to thump a precise finish into the bottom-left corner.
Valencia returned the favour in the 91st minute, sliding a throughball into Lukaku who confidently despatched past Jakupovic. Lukaku was not finished there, though, doubling his tally in the final minute of stoppage time after latching onto Omar Elabdellaoui's awful back-pass.
Key Opta stats:
- Everton have won six successive Premier League games at Goodison Park for the first time since April 2014 (7 wins).
- Romelu Lukaku (21) became the first Everton player to reach 20+ league goals in a single season since Gary Lineker in 1985-86 (30 goals).
- Lukaku is the fourth player in Premier League history to score 80+ goals in the competition before turning 24 years old (Also Michael Owen, Robbie Fowler and Wayne Rooney).
- Enner Valencia scored just 69 seconds after coming off the bench for Everton.
- No team has been shown more Premier League red cards this season than Hull City (4) - Man City and West Ham also with four.