Jack Marriott scored a last-gasp equaliser in a 1-1 draw at Rotherham to keep Peterborough in the Sky Bet League One play-off mix.Rotherham were on top in the opening stages, with Anthony Forde blowing a big chance after he was denied one-on-one by Conor O'Malley.David Ball and then Semi Ajayi were both off target with opportunities in the box.Peterborough were also wasteful in front of goal, Ryan Tafazolli and Marriott both denied by goalkeeper Marek Rodak.Driving rain affected both teams at the start of the second half but Rotherham looked more likely to break the deadlock.Caolan Lavery should really have made Rotherham's advantage count but he shot wide after the ball fell to him kindly in the box.He made amends on 68 minutes when he turned in following Forde's free-kick, which Peterborough had failed to clear.League One's top scorer Marriott remained lively well into stoppage time and he netted the leveller in the eighth added minute by turning in Junior Morias's cut-back.