After winning the toss, the Bears soon made inroads into the Lancashire batting lineup as openers Ashwell Prince (8) and Liam Livingstone (9) were dismissed with the score on 20-2 after 4.2 overs.
It didn't get much better for the visitors, with Alex Davies (2) and Karl Brown (13) departing cheaply to leave their side on 34-4 after seven overs and requiring a big innings from the middle order.
Luke Procter and Croft put on 41 in six overs to help steady the ship, before Jeetan Patel struck to remove Procter for 20 for his second wicket of the innings to leave Lancashire on 75-5 with less than seven overs remaining.
However, Croft hit three maximums to reach his fifty, while Australian all-rounder James Faulkner chipped in with 20 off 15 balls to take the score to 134-6 with six balls remaining.
Croft hit two fours to end the innings unbeaten on 64 from 51 balls to leave a Bears side, which includes Brendon McCullum, needing just over seven runs per over in their reply.