Victory would have sent Posh back to the Championship for the first time since the 2012/13 season.
Darren Ferguson’s men looked well on their way after goals from Joe Ward and Sammie Szmodics.
But Rovers, who had lost seven of their last eight games, rallied to secure a point through on-song Feriji Okenabirhie and Taylor Richards at London Road.
The hosts got off to the perfect start as they went ahead after just 10 minutes.
Nathan Thompson found Ward, who fired home a fine finish on his weaker left foot.
Josef Bursik almost gifted Rovers an instant way back when he missed a corner with Mark Beevers hacking the ball off the line. Szmodics made it two with a simple finish from Jack Taylor’s cut-back in the 23rd minute – sparking fireworks outside the ground. But the party was premature as Rovers got back into the game before the break.
Jason Lokilo found Okenabirhie as he bagged his 14th goal of the season with a low finish.
Ward came agonisingly close to restoring Posh’s two-goal cushion when he rattled the bar in first-half stoppage time.
Paul Butler’s charges threatened to find an equaliser, but it was Ward who fired against the bar once again at the other end
And those misses came back to haunt Posh as Lokilo turned defender Dan Butler before substitute Richards restored parity.
Both sides had chances to snatch all three points in an entertaining finale.
Lokilo looked certain to complete the comeback win, but shot-stopper Bursik denied him
Louis Jones produced a fine reaction save to ensure Rovers secured a point when he kept out Beevers’s powerful strike.
Lokilo was once again frustrated by Bursik in a one-on-one before Tyreece John-Jules hit the rebound over.
Peterborough: Bursik, Thompson, Kent, Beevers, Butler (Burrows, 81), Reed (Hamilton, 81), Taylor, Ward, Szmodics, Dembele, Clarke-Harris. Unused substitutes: Gyollai, Mason, Jones, Kanu, Jones, Eisa.
Doncaster: Jones, Wright, Anderson, Butler, Horton, Sims (Richards, 45), Smith, James, Lokilo, Bogle (John-Jules, 62), Okenabirhie. Unused substitutes: Bottomley, Blythe, Amos, Bostock, Greaves.
Referee: S Oldham (Lancashire).
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