Swansea missed the chance to retake the top spot in the Championship after conceding twice in stoppage time to lose 3-1 at Portsmouth.
Zan Vipotnik, the top scorer in the English second tier, looked to have rescued a point for the visitors at Fratton Park when he cancelled out Terry Devlin's opener five minutes from time.
But Devlin restored Pompey's lead before Tommy Waddingham’s 98th-minute strike ensured Middlesbrough remain top ahead of their trip to Wrexham on Wednesday.
Birmingham took advantage of Swansea's defeat to move into second place with a 3-0 win over Millwall.
Alex Cochrane, Max Bird and Jay Stansfield all struck before half-time as the Blues extended their unbeaten home start to seven games.
Southampton's promotion charge, despite starting the season with a four-point deduction for last season's spygate scandal, stalled in a 1-1 draw at West Brom
Sam Edozie rescued a point for Saints after Isaac Price's penalty gave West Brom a first-half lead to leave both sides in the play-off places.
Stoke climbed to third with a 2-1 win at Blackburn.
Earlier on Tuesday, West Ham sacked manager Nuno Espírito Santo.
Former Hammers midfielder Scott Parker is in line to take charge at the London Stadium and could be appointed prior to Wednesday's clash against Cardiff.