Birmingham – who were on the fringes of the play-off zone before replacing Gary Rowett with Gianfranco Zola – sat two points above the other two, but with an inferior goal difference.
Forest had a one goal advantage over Blackburn, and had scored more goals.
Rovers survival hopes soared when they took an early 2-0 lead at Brentford. The Blues also struck early at Bristol City, but Forest went in 0-0 at the break with Ipswich.
Forest came out with all guns blazing in the second half, and went on to beat Mick McCarthy’s side 3-0, while Blackburn beat the Bees 3-1.
The game at Ashton Gate was the last to finish. Blackburn fans were praying for a late equaliser from Bristol City, but it did not come.
Just 22 years after winning the Premier League, Rovers slipped down to the Third Tier for the first time in nearly 40 years.
Old foes, Millwall, came from behind to beat Scunthorpe at Glanford Park. The Lions secured another Wembley appearance with a 3-2 win.
Neil Harris’ side will meet Bradford City for a place in the Championship, after the Bantams drew 0-0 at Fleetwood.
The loser will again compete in League One in 2017/18, along with one from Luton, Exeter, Carlisle and Blackpool.
Luton travel to Blackpool for the first leg of the play-off semi-final on Sunday, while Exeter will make the long trek to Carlisle.
Both games will be evening kick-offs, the scheduling could hardly be worse for travelling fans.
With Plymouth, Doncaster, Rotherham and Wigan already added to next season’s list of opponents, Charlton and Gillingham fans will look at the list of midweek away games with trepidation when the fixtures come out next month.