Eisa opened the scoring in the League One fixture at Gresty Road and then won a penalty early in the second-half. He took a weak spotkick which was saved, but MK won 4-1 to move up to seventh.
Another ex-Posh forward Kyle Vassell was on target for Cheltenham in a 2-2 home draw with Sheffield Wednesday, while Danny Andrew, a full-back, scored his fifth goal of the season in Fleetwood’s 3-3 draw with Wycombe. Wycombe carelessly threw away a 3-1 half-time lead.
Conor Washington netted from the penalty spot as a resurgent Charlton side won 5-1 at home to struggling Doncaster.
In the Championship Matt Godden did his old side a huge favour by scoring the only goal for Coventry in a Championship match at Hull to increase the pressure on beleagured Tigers boss Grant McCann.
But ex-Posh loan goalkeeper Josef Bursik was not so good. His error gave struggling Cardiff their first goal in a comeback from 3-0 down to 3-3.
In League Two, former Posh midfielder Tom Conlon is leading from the front at Port Vale. The free-kick specialist and Vale skipper scored direct from a set-piece in a 4-1 League Two win at Crawley. Vale are second.
Liam Shephard assisted on Salford’s goal in a 2-1 home defeat at the hands of Exeter and Carl Piergianni claimed a consolation goal for Oldham who were beaten 3-1 at home by Swindon.
In the National League ambitious Stockport County sacked manager Simon Rusk, a former Bretton resident who was a Posh youth team player, after a 2-1 midweek defeat at home to Barnet.
And Flynn Clarke scored with a superb free-kick strike as Norwich City drew 2-2 with West Brom in an under 23 game.