The only goal of the match came early in the second period, when Danny Shittu headed home from a corner.
Mark Beevers came close for the home side after 36 minutes after the centre-back met an deep corner, but once more the Welsh side managed to clear.
Le Fondre had another golden chance for the visitors late in the half, but the former Reading striker fired straight at Forde, who had also denied Craig Noone moments before.
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The second period started in the same fashion as the first, with both sides struggling to find that elusive pass in the final third.
Millwall were ahead after 54 minutes, however, when powerful centre-back Shittu thumped a header past David Marshall from close range.
The home side had the chance to score a second just before the hour mark when Lee Gregory advanced into the Cardiff box, but his effort landed onto the roof of the net.
Gregory had another golden chance 25 minutes from time after meeting a loose save from Marshall, but once more he missed the target.
Cardiff came close to a leveller after 85 minutes when Ravel Morrison danced into the Millwall box before finding Anthony Pilkington, but his effort was blocked. Down the other end, Ed Upson fired just wide for the hosts.
The miss was not costly, however, as the hosts held on for their first league win since the end of August.