Reading produced an impressive display at St Andrew's to beat Birmingham and leapfrog their promotion rivals to move into second spot in the Championship.
Noel Hunt opened the scoring for the visitors with a whipped free-kick, but Kevin Phillips levelled against the run of play with a 25-yard drive.
Kevin Doyle restored the Royals' lead, though, with a fine glancing header.
And Kalifa Cisse wrapped things up in the 82nd minute with a bullet header as Reading made it five wins on the trot.
Birmingham manager Alex McLeish:
"We had chances but Reading were more clinical than us and it's obviously disappointing.
"But it doesn't decide anything. They are above us in the table on December 20 but the league will go right to the wire.
"They are an efficient side who do the simple things well. They are not a beautiful passing side but they all know what they are doing and they're hard to beat."
Reading boss Steve Coppell:
"This was a pleasing result but all of the players are aware that it's just one part of a demanding Christmas programme.
"One win doesn't make anything happen and we have to back it up. I hope it will be a psychological boost but only time will tell.
"The top three all had the same record over the last six games so this was an important win. We knew we'd have to play well to get a result and we did."
Birmingham: Maik Taylor, Parnaby, Jaidi, Queudrue, Murphy, Larsson (Bent 75), Carsley, Quashie, McFadden (Owusu-Abeyie 70), Phillips, Jerome.
Subs Not Used: Doyle, Hunt, Agustien.
Booked: Queudrue.
Goals: Phillips 60.
Reading: Federici, Rosenior, Duberry, Ingimarsson, Armstrong, Henry (Gunnarsson 75), Cisse, Harper, Stephen Hunt, Doyle, Noel Hunt (Long 27).
Subs Not Used: Andersen, Matejovsky, Bikey.
Booked: Rosenior, Federici.
Goals: Noel Hunt 13, Doyle 66, Cisse 82.
Att: 19,695
Ref: Mike Dean (Wirral).
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