In a game that lacked much of the bite and energy that so often lights up a local derby, Blackburn fans had to wait until the 95th minute for the one moment of real quality.
It came from a throw in, with the ball recycled back to Cashin out wide on the left at the second phase, with the defender sending in a deep cross.
Ohashi, one of the smallest players on the pitch, found himself in plenty of space to leap high and send a looping header back across goal and into the corner beyond Preston keeper David Cornell.
It sparked wild celebrations with O'Neill, taking charge of his first home game for the club, slipping over on the turf. He and his players knew what a huge moment it could be.
After a drab first half, it was Rovers who showed more attacking intent in the second, with Matias Jorgensen and Moussa Baradji going close for the hosts.
North End's attackers had a subdued evening, rarely testing Blackburn goalkeeper Balasz Toth, although they did strike the woodwork within two minutes of the start of the match.
Devine's deep corner evaded everyone and bounced up off the top of the crossbar and over, before Lewis Dobbin drew a rare save from Toth with a jinking run into the box and shot towards the near post.
Devine came within a whisker of opening the scoring directly from a set-piece again, this time whipping a dangerous free-kick into the area, which somehow squeezed all the way through and just kissed the post as it went behind for a goal-kick.
Paul Heckingbottom's side enjoyed a brief period of dominance after the introduction of Thierry Small just before the hour but ultimately missed a chance to strengthen their play-off credentials.
Having sat sixth on 94 minutes, they could find themselves as low as 12th in a congested Championship table if results go against them on Saturday.
Image source, Getty Images
