Derby, who finished fourth in the First Division, must now win twice at London's Islington venue this week to reach the play-off weekend at Wembley arena on 1 and 2 May.
Samuels scored from inside the half-way line with two seconds remaining to tie the scores on 80-80 and force overtime.
London's England quartet of Ronnie Baker, Joel Moore and the Scantlebury brothers, Peter and Richard, had regained control for London after Derby led at half-time and the visitors opened an 89-82 lead after three minutes of the extra period.
But another Samuels three- pointer followed by his two free- throws cut London's lead and the Derby player-coach Terry Manghum pulled them back again to lead 93-91.
Baker scored two free-throws to give London the margin to survive a Samuels dunk off the final play of the game.
In the other play-off openers, League champions Worthing won 84-63 at Leicester. Nigel Lloyd scored 37 points to lead Thames Valley Tigers to a 112-85 win at Oldham.Reuse content