Leyton Orient avoided an FA Cup upset to win 4-2 at Alfreton Town and book a third round trip to Hull City.

Orient endured a terrible start to the match when Paul Clayton fired the hosts into the lead. The visitors were very lucky not to concede further goals as Alfreton struck the post and bar in quick succession.

But the East Londoners equalised through Dean Cox's strike and David Mooney's finish gave them a lead they scarcely deserved after 30 minutes. A superb header from Mooney turned the tie completely around before the end of the half.

Alfreton started the second period superbly and were rewarded with a goal from Ben Tomlinson which kept them firmly in the contest.

The non-league side had their chances but Orient struck late on through Cox again to seal their place in the next round despite a very uncomfortable afternoon.

The O's made just one change from the side which beat Preston with Gary Sawyer suspended after picking up a fifth booking. Fulham gave late permission for loanee Alex Smith to feature so he made his debut in defence.

Orient were stunned after the Conference Premier side took a fourth minute lead. Nathan Arnold set up Clayton and the striker fired a low effort underneath the body of Ryan Allsop.

The League One side had their first effort on goal through Martin Rowlands' free-kick but his effort flew harmlessly wide of the target. 

Orient were looking shaky at the back and Allsop had to be quick off his line to stop Clayton getting a touch on the ball.

The hosts came so close to doubling their lead through Tomlinson but his powerful strike cannoned off the post.

The O's were shellshocked by Alfreton's start and again they were fortunate not to concede when Josh Law's free-kick took a deflection and struck the crossbar. 

Orient punished Alfreton and equalised with their first effort on target. Cox picked up the ball on the right wing, cut inside and fired a shot into the corner of the net.

It was a flattering scoreline for Orient who could have easily found themselves 3-0 down.

The goal certainly lifted the visitors and Lloyd James stung the fingers of Jon Stewart with his fierce strike. 

Orient took the lead for the first time, after half an hour, when a Lee Cook corner fell perfectly for Mooney who netted from close range.

The visitors made it 3-1 when in-form Mooney pounced again to send his header from Cook's cross past Stewart in the Alfreton net. 

It could have been 4-1 before half-time when Mooney nearly completed his hat-trick but his strike was parried by Stewart. 

The hosts came out fired up after the restart and pulled one back when a corner was not cleared and Tomlinson fired the ball past Allsop.

It was so nearly 3-3 minutes later but Tomlinson's effort struck the bar and Orient once again breathed a huge sigh of relief. 

Alfreton kept up the pressure and skipper Darran Kempson was only denied an equaliser when his effort was cleared off the line. 

Orient had hardly had a kick in the second half but they almost netted a fourth with their first attack. Smith's cross was headed towards goal by Kevin Lisbie but a defender blocked the effort. 

Slade made his first change as he introduced midfielder Jimmy Smith in place of Lee Cook. 

The hosts kept pushing for an equaliser and were again desperately unlucky when Law's free-kick cannoned off the bar.

Alfreton were harshly punished on the break in the 86th minute as Mooney set up Cox for a cool finish to ensure Orient's place in the next round. 

Alfreton Town: Stewart; Law, Franklin, Kempson, Bradley; Streete, Killock, Meadows (Emerton, 90), Clayton (Worsfold, 90); Arnold, Tomlinson (Denton, 82)

Subs not used: Barnes, Quinn, Brown, Russell

Leyton Orient: Allsop; Smith, Chorley, Baudry, Odubajo; James, Rowlands, Cook (Smith, 79), Cox; Lisbie (Brunt, 90), Mooney

Subs not used: Jones, Cuthbert, McSweeney, Griffith, Symes

Referee: Robert Madley

Attendance: 1,104