The midfielder, who ended a 13-month goal drought against Coventry on Good Friday, lashed home the opener before doubling Posh's lead after Alex keeper Ben Garratt had denied Aaron Williams.
Lee Angol sealed United's third straight win with a rasping finish from Marcus Maddison's fine pass.
The visitors offered little as their winless run stretched to 11 games.
Crewe are now 12 points from safety with just six games to go, while Peterborough stayed 14th.
Harry Beautyman scored twice as Peterborough edged League One basement side Crewe closer to the drop.