The Bluebirds fielded the side that beat Leicester last week but Glenn Loovens had recovered from injury to take a place on the bench.
City had all the early pressure and a Rhys Weston cross was put behind for a corner with Jerome closing in.
A piece of a Jason Koumas trickery opened up the Lions defence at the expense of yet another flag-kick when Steve Thompson's header drifted wide of the far post.
In the 20th minute a Chris Barker cross was met by Thompson but his downward header grazed the outside of the stanchion.
City broke the deadlock in the 28th minute with a superb strike. Riccardo Scimeca slipped a pass into Koumas who sent Jerome racing down the middle. His low finish struck the back of the net before Lions keeper Andy Marshall could move.
A minute before the interval Thompson fed Jerome but his lob cleared the Millwall crossbar.
There was still time for a mazy run by Koumas who again picked out Jerome but the much sought after striker hurried his shot and sent it spinning wide.
Three minutes after the restart Jerome fell in the box after a clumsy challenge but the referee waved play on when it looked a certain penalty.
In the 57th minute Berry Powel came on for his debut up front as the Lions looked to get back into the game.
He was immediately into the action, slipping between the Cardiff centre-backs but his shot was well wide.
But the former Den Bosch man made no mistake in the 60th minute when he turned Weston before firing in the equaliser low into the corner of the net.
Weston was replaced by Kevin Cooper in the 83rd minute after coming under increasing pressure from the Millwall left flank.
City forced three corners in time added on but could not find the opening and had to be content with the draw.