Brighton grabbed an injury-time winner to reach the playoffs and Birmingham also scored with seconds remaining to avoid relegation on a dramatic final day in the second-tier League Championship on Saturday.
Brighton will compete for a place in the Premier League for the first time with Derby, Queens Park Rangers and Wigan after finishing sixth in the Championship by beating Nottingham Forest 2-1 thanks to Leonardo Ullua's goal two minutes into added time.
Reading drew 2-2 at home to Burnley and finished a point behind Brighton in seventh.
In the two-legged playoffs, Brighton will play Derby and QPR will play Wigan. The final is at Wembley Stadium on May 24.
Three years after winning the League Cup, Birmingham faced the prospect of demotion to the third tier but Paul Caddis scored in the third minute of stoppage time to claim a 2-2 draw at Bolton and consign Doncaster to the drop on goal difference.
Doncaster lost 1-0 at Leicester, which had already gained automatic promotion to the Premier League with Burnley.
