Match ends, Birmingham City 0, Derby County 4.
Derby County climbed up to third in the Championship with a convincing win over Birmingham City.
Jordon Ibe's solo effort and Chris Martin's 20-yard free-kick set the Rams on their way in the first half.
Blues improved slightly after the break and substitute Wes Thomas forced Lee Grant into a smart stop.
But Craig Forsyth, who scored at St Andrew's in a 3-3 draw last season, and Johnny Russell sealed the victory with late strikes.
Derby had started December as the Championship leaders, but could have been forgiven for lacking in confidence after dropping down to fifth following a defeat by Middlesbrough and a draw against Norwich City.
|Derby's six away wins this season is equal best in the Championship, along with Bournemouth and Middlesbrough|
However, any fears of that minor wobble becoming anything more substantial were brushed aside with a fluent performance.
Midfielder Will Hughes dictated the pace for the Rams, who started confidently and were in front after seven minutes when teenager Ibe, on loan from Liverpool, skipped past a series of Birmingham defenders and fired past keeper Darren Randolph.
Russell was denied by Randolph when through one-on-one, but Martin affirmed Derby's first-half dominance by thrashing a free-kick into the net for his 16th goal of the campaign.
Blues boss Gary Rowett, who played 120 times for Derby between 1995 and 1998, has overseen a tremendous improvement in his two months in charge at St Andrew's, but his side were uninspiring in what was only their second defeat of his tenure.
With snow teeming down in the West Midlands, Birmingham made a rare chance as substitute Thomas drew a sharp save from Grant in the second half.
Randolph once again thwarted Russell at the other end as the game opened up, but Forsyth finished from 20 yards after a one-two with Ibe and Russell cut in and lashed home to cap off a productive trip.
Derby boss Steve McClaren: "From the beginning we were always in control. We dug in when we had to on occasions.
"We have talked about being ruthless and they were and it could have been a lot more. I couldn't fault how we want to play and it was a great result."
Birmingham manager Gary Rowett: "I actually thought Derby were the most clinical and threatening side that we have played in the last eight we've played.
"They showed their quality and class. Their wide players were a constant threat throughout the game."
- 11CotterillSubstituted forThomasat 58'minutes
- 8GleesonBooked at 22mins
- 22ShinnieSubstituted forZigicat 58'minutes
- 9DonaldsonSubstituted forNovakat 87'minutes
- 8HendrickSubstituted forCouttsat 66'minutes
- 14EustaceBooked at 6mins
- 19HughesBooked at 43mins
- 9MartinSubstituted forBestat 86'minutes
- Chris Foy
- Shots on Target
Second Half ends, Birmingham City 0, Derby County 4.
Attempt missed. Lee Novak (Birmingham City) right footed shot from outside the box misses to the left. Assisted by Nikola Zigic with a headed pass.
Goal! Birmingham City 0, Derby County 4. Johnny Russell (Derby County) left footed shot from the right side of the box to the bottom left corner. Assisted by Leon Best.
Substitution, Birmingham City. Lee Novak replaces Clayton Donaldson.
Substitution, Derby County. Leon Best replaces Chris Martin.
Attempt missed. Clayton Donaldson (Birmingham City) header from the centre of the box is high and wide to the left. Assisted by David Davis with a cross.
Attempt missed. Demarai Gray (Birmingham City) left footed shot from the right side of the box is too high. Assisted by Paul Robinson.
Foul by Ryan Shotton (Derby County).
Nikola Zigic (Birmingham City) wins a free kick in the attacking half.
Foul by Cyrus Christie (Derby County).
Clayton Donaldson (Birmingham City) wins a free kick on the left wing.
Goal! Birmingham City 0, Derby County 3. Craig Forsyth (Derby County) right footed shot from outside the box to the bottom right corner. Assisted by Jordon Ibe.
Foul by John Eustace (Derby County).
Stephen Gleeson (Birmingham City) wins a free kick in the defensive half.
Corner, Derby County. Conceded by Paul Robinson.
Foul by Craig Forsyth (Derby County).
Demarai Gray (Birmingham City) wins a free kick in the defensive half.
John Eustace (Derby County) wins a free kick in the defensive half.
Foul by Nikola Zigic (Birmingham City).