Boss Paul Warne described himself as "incandescent with rage" after two Rotherham United blunders handed Peterborough United a 2-1 League One win at the ABAX Stadium.
Goalkeeper Richard O'Donnell allowed a cross-goal shot from Jack Marriott to beat him and then Semi Ajayi failed to deal with a routine long ball and let Marriott in for a second.
"We created enough chances to win the game three times over," said Warne who saw loan striker Kieffer Moore score his fourth goal in two games for the Millers.
"You just can't legislate for individual errors. I am incandescent with rage.
"When we got back to 1-1, I thought we would go on to win the match."
The Millers gave a good account of themselves in the end-to-end clash against unbeaten Posh.
Moore, who bagged a hat-trick in the 5-0 triumph over Southend United last week, had brought them level with a powerful header on 55 minutes following Marriott's 47th-minute opener.
Ajayi's 75th-minute error was the key moment in the encounter.
"I think the scoreline is a bit harsh on us," Warne added. "The game went they way I thought it would do beforehand. It was end to end.
"I'd like to thank our fans. They were brilliant and loud."
Both sides hit the woodwork in an entertaining first half that should have brought goals as two dangerous teams attacked each other.
Posh dangerman Jack Marriott smacked the bar from Anthony Grant's long ball after eight minutes and Kieffer Moore hit the post in an amazing 24th-minute sequence of play which saw the Millers denied four times.
Home goalkeeper Jonathan Bond saved well from Ryan Williams and then kept out Jamie Proctor's follow-up effort from a tight angle, Lee Frecklington was thwarted by a crucial block and Moore looked to have put the visitors ahead as the ball broke to him only for his cross-goal shot to hit the inside of the upright and stay out.
Proctor had a free header in front of goal from Williams' cross in the 13th minute but mistimed his leap and failed to connect, while O'Donnell had to produce a sharp save from Leo Da Silva Lopes six minutes before the break.
Rotherham pressed for a leveller in the closing stages.
Moore had a header pushed for a corner and Frecklington headed wide but the Millers couldn't equalise for a second time.
Goals: Marriott 47, 75 (Peterborough); Moore 55 (Rotherham).
Peterborough (3-4-1-2): Bond; Taylor, Baldwin, Tafazolli; Da Silva Lopes (Hughes 81), Doughty, Grant, Edwards; Maddison (Forrester 81); Morias (Kanu 71), Marriott. Subs not used: O'Malley, Shephard, Lloyd, Borg.
Rotherham (4-4-2): O'Donnell; Emmanuel (Forde 81), Ajayi, Ihiekwe, Mattock; Williams (Taylor 75), Potter, Frecklington, Newell; Moore, Proctor (David Ball 71). Subs not used: Bilboe, Vaulks, Purrington, Clarke-Harris.
Referee: Ross Joyce (Cleveland).
Attendance: 6,344 (1,068).