Millwall extended their winless league run to four matches when they suffered a 2-1 defeat away against Hull City last weekend.
Tom Bradshaw’s strike in first-half stoppage time cancelled out George Honeyman’s opener, however the hosts regained the lead seven minutes after the break through Ryan Longman and were able to hold on for all three points.
Gary Rowett’s men remain 10th in the Championship standings, but the gap between them and the playoffs has now increased to six points.
Millwall have struggled defensively in recent weeks, keeping only one clean sheet in their last nine league games. The Lions will, however, be confident of keeping Birmingham’s attack quiet on Saturday
as they have kept seven clean sheets in their last nine league matches against the Blues, including shutouts in both encounters last season.
Rowett’s side also have an impressive record on home soil, losing just one of their last eight Championship matches at The Den, as well as scoring in each of their last 12 games in front of the Lions faithful.
Birmingham ended a run of three league games without a win when they secured a slender 1-0 win at home against high-flying Blackpool last weekend.
After a goalless first half, the deadlock was eventually broken in the 81st minute when substitute Lukas Jutkiewicz bundled the ball in from close range, netting just his second goal of the campaign.
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That result has seen the Blues climb three places up to 14th in the Championship, 10 points clear of the relegation zone and seven behind the top six.
Lee Bowyer’s men travel to Millwall on Saturday after winning only one of their last eight league games away from home and failing to score on six occasions in the process.
Following a 2-0 loss at The Den last season, Birmingham will be hoping to avoid successive league defeats at Millwall for the first time since losing in 1994 and 1996 under former boss Barry Fry.