Rotherham suffered a sixth successive defeat as Peterborough battled to a 2-0 League One win at the New York Stadium.
Both Posh’s goals came in the second period and lifted them further away from trouble as their unbeaten streak extended to six matches.
Rotherham came close to going ahead when Denzel Hall cut back a cross which Kion Etete acrobatically sent towards goal but into the arms of Alex Bass.
Peterborogh’s Matthew Garbett then forced Cameron Dawson into a save with a stinging free-kick.
The Millers made a bright start to the second half with substitute Ar’jany Martha supplying Dru Yearwood who saw his curling effort turned behind by Bass.
Peterborough then rattled the upright with a powerful effort from Donay O’Brien-Brady.
Jordan Hugill struck the bar at the other end after he latched onto Shaun McWilliams’s chip.
Peterborough turned the game in their favour in the 61st minute with Declan Firth putting in a cross which rebounded off Joe Rafferty and across the line.
They sealed victory in the 73rd minute with substitute Brandon Khela expertly shooting into the bottom corner from the edge of the box.
Subscribe or register today to discover more from DonegalLive.ie
Buy the e-paper of the Donegal Democrat, Donegal People's Press, Donegal Post and Inish Times here for instant access to Donegal's premier news titles.
Keep up with the latest news from Donegal with our daily newsletter featuring the most important stories of the day delivered to your inbox every evening at 5pm.