Sky Bet League One leaders Peterborough tumbled to their first defeat in nine games as first-half goals from Harry Pickering and Charlie Kirk secured Crewe a shock 2-0 win.
Without a point from their previous three games, Dave Artell's side deserved their victory after dominating the first half at Gresty Road and repelling what little Posh had to throw at them after the break.
Oli Finney should have done better with an early header he directed the wrong side of the post after Tommy Lowery floated a tantalising cross into the six-yard box.
But the midfielder was inches away from finding the bottom corner with a low drive shortly afterwards and he was involved when Crewe took a 29th-minute lead. His driving run onto Ryan Wintle's pass was brought to a halt on the edge of the box by Louis Reed's ill-judged tackle.
Pickering showed his prowess from the dead ball, stepping up to drive a left-footed finish across goalkeeper Christy Pym and into the bottom corner via the inside of a post.
The leaders struggled to get out of their own half in the first period, such was Crewe's accurate passing and the determination of their press.
Crewe keeper Will Jaaskelainen was untroubled, save from when he shepherded Joe Ward's tame effort around a post.
Posh's plight deepened when Niall Mason's risky cross-field pass was intercepted by Kirk, who raced clear and thrashed the ball into the corner beyond Pym for Crewe's second four minutes before the break.
Darren Ferguson's side improved in the second half but posed a limited threat. Defender Dan Butler fired an angled drive past a post.
Their best chance fell to substitute Mo Eisa after Jaaskelainen pushed out Reece Brown's long-range effort. But Eisa failed to make the most of the loose ball and his miss-hit follow-up was blocked by the keeper.