The steward tussled with a fan while trying to clear fans off the playing area at Deepdale and was pushed to the floor, with the police horse riding straight over him moments later.
The fan he clashed with immediately backed away while apparently filming the incident on his mobile phone, as the screen grab sequence below appears to show.
The steward sustained a shoulder injury and was taken to hospital for X-rays.
"This is the problem in football and we talk about the respect campaign and you see enough incidents in football where fans are allowed to run on the pitch," an angry Blackpool manager Paul Ince told the BBC.
"We've seen goalkeepers get hit and players get punched. When are we going to learn?"
Ince labelled the scenes an "absolute joke" and added: "I understand that fans get excited....but who knows what can happen.
"We're not listening. Has someone got to be stabbed before we listen?"
The former England international continued: "I wondered if we have enough stewards.
"You see enough situations where fans run on a pitch and I can understand fans' excitement, but there have been enough frightening things that have happened to players that we need to stamp down on it.
"There were three or four hundred Preston fans, so who knows what could have happened? Has it got to take something else to happen before we listen? That's not just Preston but it's the whole football community in general. We need to knuckle down on this.
"We're disappointed as our fans were absolutely fantastic and their behaviour was impeccable. There were no louts on the pitch - unlike Preston - and we conducted ourselves in the right manner. We have to take pride from that as a club."
Tom Ince could have put Blackpool ahead when he found himself through on goal but his 18th-minute shot from just inside the area was off-target.
Angel Martinez went agonisingly close for Blackpool in the 50th minute after his header from Kirk Broadfoot's cross went inches wide.
Iain Hume then nearly put Preston ahead with his 63rd-minute shot that Matt Gilks did well to push around his post.
Michael Chopra had a golden chance to give Blackpool the lead but his 72nd-minute header bounced into the pitch and over the bar.
The Seasiders pushed again and Bobby Grant's corner found Broadfoot but the defender headed over and, with Clarke capitalising moments later, the Championship side crashed out.
- Sports & Recreation
- pitch invasion
- Paul Ince