Bassala Sambou's stoppage-time goal sent O's out of the FA Cup, after Craig Clay was sent off in the closing stages at Gresty Road.

Richie Wellens made a host of changes from the previous weekend's 1-0 win over Salford City in League Two for the first-round tie, with Joel Tabiner sending an early free-kick over the crossbar for the home side.

Ruel Sotiriou controlled a George Moncur flick-on but dragged his shot just wide on four minutes, while Charlie Kelman had the ball in the net moments later but saw it harshly ruled out for a foul.

Moncur fired at Arthur Okonkwo, who tipped a Kelman drive behind as the visitors remained on top.

And Stephen Duke-McKenna was also denied by the Crewe keeper, before Lawrence Vigouroux was called into action for the first time on 15 minutes to save Dan Agyei's header.

Moncur skewed a shot over on 24 minutes, after a break on the right by Sotiriou, and was then pulled back by Conor Thomas, who picked up the first yellow card of the tie.

And the midfielder was inches away from giving O's the lead on 32 minutes when receiving the ball from a short corner, advancing into the box and firing against the crossbar.

A low Duke-McKenna drive was deflected behind by Kelvin Mellor, while Lachlan Brook missed the target for the hosts from the edge of the box.

And Sotiriou fired wide from a tight angle two minutes before the interval as the scoreline remained blank and heavy rain began to fall.

O's controlled possession without creating many notable chances in the early stages of the second half, before Wellens sent Paul Smyth and Theo Archibald on for Sotiriou and Duke-McKenna just before the hour.

Shad Ogie was booked for a foul on Mellor, with Tabiner heading wide from the resulting Crewe free-kick, and Wellens made another double change midway through the half as Idris El Mizouni and Aaron Drinan relieved Moncur and Kelman of their duties.

Archibald fired straight at Okonkwo from outside the box on 70 minutes, with El Mizouni seeing his attempt blocked at the expense of a corner.

And O's saw another effort ruled out when Smyth found the net, only to see an offside flag had gone up, before the Irishman cut inside and saw a goalbound shot blocked on 82 minutes.

Ogie's excellent tackle denied Agyei at the other end, but O's were reduced to 10 men three minutes from time when Clay was shown a straight red card by referee Sam Purkiss for a challenge on Brook.

And they were made to pay as Sambou struck in the second minute of injury time to send Crewe into the second round.

Leyton Orient: Vigouroux, James, Ogie, Clay, Sotiriou (Smyth 58), Brown, Moncur (El Mizouni 67), Beckles, Kelman (Drinan 67), Hunt, Duke-McKenna (Archibald 58).
Unused subs: Sargeant, Happe, Wareham, Pratley, Sweeney.