Tom Eaves' goals were his fifth and sixth of the season
Rotherham secured just their fifth league win of the season as they enjoyed a 5-2 thumping of Cardiff City at a sunny New York Stadium.
The hosts led at half-time as former Bluebird Jordan Hugill and Tom Eaves scored either side of a Nat Phillips header.
Ollie Tanner’s second goal of the season levelled for Cardiff, but the hosts took control thanks to Eaves’ penalty and an excellent curling effort from Sam Nombe.
Hugill added his second from a woeful Phillips backpass as Rotherham secured a first final-day win in the second tier since 1967 and in the process recorded their biggest win of the season.
The Millers still finish bottom of the Championship, while defeat means Cardiff finish their campaign 12th.
On a day of high stakes and drama in the Championship this was a low-key contest with Rotherham relegated and Cardiff City safely ensconced in mid-table.
Cardiff have opened talks with boss Erol Bulut about a new deal and the Turkish boss would have been looking to sign-off for the season on a high note for a Cardiff side that have enjoyed recent visits to Rotherham.
Rotherham came into this content winless in eight league games against Cardiff, with the Bluebirds winning their last three away league visits to the Millers.
It has been a miserable campaign for the Millers whose four wins from 45 Championship games meant they came into the contest hoping to avoid equalling the record low number of wins in a 46 game season, with Blackpool also only winning four times in 2014-15.
The Millers took the lead against the Bluebirds in a first period desperately short of action in the final thirds and never looked back as they produced one of their best displays of the season.
It was from the first effort on target by either side that Rotherham went ahead on 25 minutes as Hugill tapped-home against his former club after finding space to convert Cohen Bramall’s cross.
The goal stirred both sides into life with Eaves heading wide with a chance to double Rotherham’s advantage, while Dillon Phillips saved against his former side to deny both David Turnball and Josh Bowler.
The Bluebirds eventually levelled through their usual route to goal, a set-piece, with Phillips stooping to head home from Tanner’s fine delivery on 38 minutes.
It was the hosts, however, who edged back in front before the break as Eaves converted a sharp chance from the edge of the penalty box after more sharp work from Bramall.
A chance to earn just a fifth win for the Millers this term, however, suffered a blow within seconds of the restart as Tanner’s deflected effort found the bottom corner of the net.
But it was Rotherham who took control with the game level, and they won a 57th minute penalty after David Turnball’s foul, and Eaves kept his composure to fire home.
The goal buoyed the hosts and they scored a fourth on 63 minutes as Nombe curled home beautifully from the edge of the penalty box.
Hugill then scored his second as he took advantage of Phillips’ woeful backpass, with the striker also firing against the upright as he chased a hat-trick and heading wide in added on time.
Rotherham boss Steve Evans told BBC Radio Sheffield:
“We’ve only spoken about positivity. The players were surprised when we told them we were playing with three strikers, but we thought that was a way we could get at Cardiff City.
“A lot of the boys had a big performance today. We wanted to go out playing the Rotherham United way, with lots of passion and commitment.
“The supporters deserve the credit today for turning up and supporting us after being relegated and the players [deserve credit].
“We will come back regrouped and recharged.”
Cardiff City boss Erol Bulut told BBC Radio Wales:
“It was a disappointing end, but the referee helped the result a lot…he didn’t have a good day today.
“We tried to come back, but it was not really a game where we created the chances we needed.
“Without the ball we didn’t produce what we were expecting.
“I believe we can build here, much, much better things.”
