Riley McGree returned to haunt his old loan club Birmingham with a stunning goal as Middlesbrough won 1-0 at St. Andrew's.
Attacking midfielder McGree, 25, put Boro ahead in the 17th minute after a mistake by Alex Pritchard in a game of few clear-cut chances.
The result heaps pressure on City, who have now gone five games without a win and are only out of the Sky Bet Championship relegation zone by a point after their match in hand.
City have not won since manager Tony Mowbray - a much-loved former Middlesbrough player and manager - has been away from his daily duties for medical treatment.
Both sets of fans chanted his name but Birmingham looked in need of the 60-year-old's guidance as Boro made it three wins in a row.
Birmingham had the first chance when Pritchard attempted a 40-yard chip over goalkeeper Seny Dieng but his ambitious effort drifted wide.
Paddy McNair fired over a long-range rising effort for Middlesbrough after Emmanuel Latte Lath was denied from point-blank range by goalkeeper John Ruddy.
But a mistake by Pritchard led to Boro taking a 17th-minute lead.
The former Brentford and Sunderland midfielder's pass was easily cut out by Luke Ayling. He found McGree, who lashed an unstoppable left-foot drive into the top corner of the net from 25 yards.
McGree, who spent 15 months on loan at Blues from October 2020 to the end of 2021, celebrated in understated fashion against his old club.
Things went from bad to worse for City two minutes later when centre-back Marc Roberts went off injured to be replaced by Cody Drameh.
Ayling tried to make it 2-0 after cutting inside and curling goalwards but his attempt was straight at Ruddy.
Pritchard sliced horribly wide on the angle as neither he nor Koji Miyoshi seemed to want to
Middlesbrough
Birmingham
soccer
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Marc Roberts
Tony Mowbray
Riley Macgree
Cody Drameh
Luke Ayling
Alex Pritchard
Paddy Macnair