Posh led 2-0 through Siriki Dembele and Sammie Szmodics but Rochdale roared back in the second half and looked to have claimed the win thanks to efforts from Stephen Humphrys (penalty), Jake Beesley and Jimmy Keohane – the latter two goals coming in the final three minutes.
But the prolific Clarke-Harris slotted home in the third minute of added time to grab a draw for promotion-chasing Peterborough.
Dale were on the back foot after just five minutes when Dembele collected the ball 25 yards from goal and launched a stunning shot into the top corner of Gavin Bazunu’s net.
The home side settled and Humphrys was close with a scissor kick which flew narrowly wide.
But they were hit with a sucker-punch in first-half stoppage time when Dembele slipped a pass to Szmodics who side-stepped his marker before finish wide of Bazunu to make it 2-0.
Dale were given a lifeline after 55 minutes when Beesley was fouled by Mark Beevers and referee David Rock awarded the home side a penalty. Humphrys stepped forward and sent Christy Pym the wrong way from the spot.
Then, in the 87th minute, the home side drew level when Matt Done’s cross was headed home by Beesley, and three minutes later they were ahead as Keohane smashed a close-range finish into the roof of the net.
But Posh grabbed an equaliser at the death when Aaron Morley fouled Nathan Thompson and Clarke-Harris converted the spot-kick.