After going behind, Blackpool bounced back and looked to have won it, but Kane's goal means they go into the Championship play-offs playing the crucial second leg away from home.
The home side came racing out of the blocks and had their first chance after a minute. The ball fell to Andy Keogh, who had scored four in the previous five games, but his effort from 20 yards flashed wide.
Millwall, the form team in the Championship with five consecutive wins, continued to press and Blackpool were indebted to Matt Gilks as he pushed away a powerful strike from Kane at his near post.
Their early dominance was rewarded after 12 minutes thanks to the in-form Keogh. He beat the offside trap to latch onto a James Henry pass and coolly side-footed past the helpless Gilks.
Blackpool had the woodwork to thank for not falling further behind. Henry crossed to the unmarked Paul Robinson three yards out who inexplicably headed against the bar.
Out of nothing, Ian Holloway's side levelled after 27 minutes with their first attack of the game. Stephen Crainey whipped a free-kick towards Ian Evatt whose diving header beat Maik Taylor.
That goal, only the second Millwall have conceded in over six games, seemed to knock the stuffing out of the hosts, who found chances harder to come by.
Ince missed a glorious opportunity just before half-time. Nouha Dicko intercepted a poor back pass and set up Kevin Phillips, who in turn laid the ball into Ince's path but the ball went wide from seven yards.
The Seasiders continued where they left off and Kevin Phillips tested Taylor with a rasping drive from the right of the area, which the goalkeeper did well to hold.
Millwall settled and were agonisingly close to going ahead midway through the half. A Henry corner was met by Liam Trotter, whose header was saved by Gilks and the clearance was completed by Crainey.
But Blackpool caught the Lions cold for the second time in the day just minutes later. Ince and Crainey combined for the latter to send in an inviting cross towards Dicko who could not miss.
The goal sparked Millwall into life and they were rewarded when a corner was only half cleared to Kane on the edge of the area and he rifled a shot into the bottom-left corner.
Millwall almost grabbed a late winner but Evatt made a timely intervention to ensure the game ended level, meaning both sides are unbeaten in their final seven games.