Dunn has been the key behind Birmingham's recent revival, and the Blues' 2-0 victory against Middlesbrough was their third successive win.
His form has also helped Clinton Morrison and Emile Heskey emerge as a dangerous strikeforce. This was evident as the duo scored the two first-half goals which paved the way for their latest win.
Dunn only lasted 54 minutes and there must now be a question mark over his future this season.
Birmingham manager Steve Bruce admitted afterwards: "It doesn't look very good. Dunn's hamstring appears to have gone again, while Emile Heskey also had to come off with a hamstring.
"These injuries put us under a great deal of pressure as we are already missing Dwight Yorke and Muzzy Izzet.
"It's typical of our luck. But it was still a very good win over a Middlesbrough side which has been playing so well this season."
Boro, who last won at Birmingham in 1987, rarely appeared capable of ending this dismal record.
Manager Steve McClaren said: "I'm very disappointed. We had a great opportunity which we failed to take.
"The performance was poor and well below our usual standard. If we want to be Champions League challengers we cannot afford these sort of off-days but we can bounce back.
"It was just one of those days but it was poor defending and we allowed Birmingham too much scope."
On the back of two successive wins Birmingham were in a confident and attacking mood against high-flying Boro and this was quickly reflected in their positive start which had the Teessiders defence in all sorts of trouble.
After beating Aston Villa 3-0 with an unimpressive display, Boro were boosted by the return of Mark Viduka.
The extra firepower was evident as early as the third minute when Doriva set up Jimmy Hasselbaink but the move ended with Stan Lazaridis slicing an intended clearance into his own net only for the effort to be disallowed for offside.
Thereafter it was predominantly Birmingham who were on top with Dunn emerging as the main danger and he soon set up Morrison.
The striker's shot was goalbound but Franck Queudrue was positioned perfectly to intercept and clear what had appeared to be a potentially dangerous situation.
Boro's injury crisis has stretched their resources, and they found the Blues difficult opposition to contain in the early stages.
Heskey was a handful for his England colleague, Gareth Southgate, and his strong leadership and ever improving partnership with Morrison was a feature of Birmingham's performance.
The Republic of Ireland international, who was fourth choice at the start of the season, has recently grabbed his chance with an impressive spell of goalscoring which was demonstrated by the eager and positive way he broke the deadlock in the ninth minute.
A long free-kick from Damien Johnson was allowed to go unchecked by Queudrue and Morrison was onto the ball in a flash to fire his shot past Schwarzer.
Boro failed to respond and in the process they lost the services of Viduka which only appeared to compound their problems.
They were unable to exploit the possible shortcomings of Birmingham in midfield with Ray Parlour well off the pace.
As a result a pattern developed where Birmingham were allowed to dominate most of the attacking play as Middlesbrough attempted to frustrate the home side.
At the same time they were dangerous on the break with Stewart Downing and Doriva having a big say in building several dangerous moves.
But Boro descended into the depths of despair a minute before the break when Birmingham produced a killer second goal.
Darren Carter saw a snap-shot deflected for a corner. He then took a short corner to Robbie Savage and his cross was headed into the far corner of the net by Heskey.
The early loss of both Heskey and Dunn disrupted Birmingham but Boro were unable to take full advantage of the situation and could have few real complaints about the result.