The Devils lacked the all-round strength of the visitors, who provided 12 of the 15 race winners.
Team manager Lee Trigger said: “It was a poor show and we let the supporters down again. We did not make the starts and did not perform as a team.
“It means we will be playing catch up in the Premier League. We will have to have a good look at ourselves because we cannot afford to go on losing at home.”
Sam Simota and skipper Kyle Newman gave Plymouth a winning start in the first race but that was a rare heat win for the home side.
Former Plymouth favourite Ben Barker made a successful return to the Arena with 12 (paid 13) points as a guest for Peterborough’s injured number one Olly Allen and there were also double figure returns for visiting skipper Ulrich Ostergaard and Lewis Blackbird.
Plymouth: Kyle Newman 9+2 (5 rides), Sam Simota 9 (5), Jack Holder 6 (4), Morten Risager 5+2 (4), Ryan Fisher 4+1 (4). Reserves: Ashley Morris 6+1 (5), Ben Morley 1+1 (3).
Peterborough: Ben Barker 12+1 (5), Michael Palm Toft 8+1 (5), rider replacement for Robert Lambert, Lewis Blackbird 11+1 (5), Ulrich Ostergaard 14+1 (6). Reserves: Oliver Greenwood 0 (3), Simon Lambert 7+1 (6).