Stephen Dobbie struck twice as Swansea hammered relegated Sheffield United to clinch third place and book a play-off meeting with Nottingham Forest.
Dobbie opened with a sweetly-struck free-kick from an acute angle after Matthew Lowton fouled Scott Sinclair.
Sinclair doubled the lead from the spot after Shane Lowry saw red for handling the striker's shot on the line.
Dobbie struck again from the edge of the box, while Leon Britton grabbed a late fourth.
Swansea's play-off fate was only confirmed an hour before kick-off when over the signing of midfielder Alejandro Faurlin.
The ruling that no points would be deducted put an end to hopes of Swansea going up automatically.
Had QPR lost points, the victory of Sheffield United would have sent the Swans up and the club is considering a response to the ruling.
So they were left to battle it out with rivals Cardiff City for third place and the Swans' win, coupled with Cardiff drawing at Burnley, meant they claimed that spot to set up a meeting with sixth-placed Forest in the play-off semi-finals.
Victory rarely looked in doubt and the Swans were almost ahead in a little over a minute when Dobbie picked up on a deflected pass and drilled straight at George Long, but the 17-year-old debutant saved well.
The home side dominated but already-relegated Sheffield United had no intention of going down with a whimper.
And on 13 minutes, Michael Doyle fizzled a shot just wide of the right-hand post. Soon after though, it was the Swans who were again on the attack.
First, Dobbie put in a low cross from which Sinclair saw two attempts blocked before Nathan Dyer fired over.
Then Fabio Borini squared from the right to player-of-the-year Dyer whose six-yard effort was saved superbly at point-blank range by Long.
United gave the Swans another scare midway through the first-half when Stephen Quinn ran at the home defence before finding Williamson free in space to shoot but Dorus de Vries got a hand to it.
The breakthrough came on the half-hour when Lowton hacked down Sinclair just outside the box, which Dobbie rifled the resulting free-kick from an acute angle.
Sinclair almost doubled the lead moments later with a silky run into the box and it was only the legs of Long that kept him at bay,
But Long could do nothing 10 minutes after the restart to keep out Sinclair who converted from the spot after Lowry saw red for handling the Swans' top scorer's original effort on the line.
Sinclair stepped up to calmly put the ball beyond Long for his 24th goal of the season.
It was harsh on youngster Long who found himself picking the ball out of the net again moments later as Dobbie blasted his ninth goal of the season.
And to rub salt into United's wounds, Britton who signed for the Blades in the summer before returning to south Wales seven months later, claimed his first goal of the season in the final minute.