Non-league Chesterfield pulled off a shock 2-0 win at AFC Wimbledon to book their place in the FA Cup third round. Armando Dobra put the National League high-flyers in front just before half-time and Jeff King’s long-range effort with 15 minutes left made sure of the upset against the League Two side. Paul Mullin scored a hat-trick as Wrexham, the National League leaders, defeated Farnborough 4-1 at the Racecourse Ground. Mullin headed the Dragons in front from a corner early in the second half, but the National League South visitors were level just after the hour through a free-kick from Oli Pendlebury. Elliot Lee put Wrexham back in front with 12 minutes left before Mullin added two more late on to complete his treble. Forest Green Rovers ended seventh-tier Alvechurch’s hopes of a money-spinning tie in the third round with a 2-1 win. The former Crystal Palace striker Connor Wickham put Rovers, who are bottom of League One, ahead from the penalty spot in the 24th minute. Alvechurch – who play in Southern League Premier Central Division and were the lowest-ranked team left in the competition – equalised three minutes into the second half through Jediah Yeboah Abbey’s free-kick. However, Josh March put the League One side back in front just two minutes later, scoring against his former club. Forest Green finished the match with 10 men after the defender Dom Bernard was sent off for a second yellow card after grabbing Danny Waldron’s shirt as the Church striker looked to break clear. King’s Lynn, second-placed in National League North, were beaten 3-0 at home by Stevenage of League Two. Three goals in five minutes at the start of the second half, with Luke Norris scoring a quickfire brace before Jamie Reid’s strike, ended the Linnets’ hopes of further progress. Barnet’s cup dreams were ended with a 1-0 defeat for the National League side at Accrington through a late goal from Ethan Hamilton. Otis Khan hit a last-minute winner as Grimsby stunned Cambridge 2-1 at the Abbey Stadium. Khan had put the League Two visitors ahead on the hour, but Sam Smith nodded in a equaliser before the Mariners frontman struck a late second to send the League One Us crashing out. Myles Hippolyte headed a stoppage-time equaliser as League Two Stockport snatched a 2-2 draw at Charlton to earn a replay. Chris Hussey had given County an early lead but the Addicks led by half-time, Steven Sessegnon’s cross diverted into his own net by keeper Ben Hinchcliffe before Albie Morgan made it 2-1. Goals from Devante Cole, Adam Phillips and a Josh Benson penalty gave Barnsley victory against Crewe of League Two 3-0 at Oakwell. A brace from Josh Umerah helped Hartlepool beat 10-man Harrogate 3-1 at Victoria Park. The Town defender Joe Mattock was sent off at the end of the first half for a foul on Umerah, who slotted in the resulting spot-kick. Billy Bodin grabbed two goals in the closing stages as Oxford beat their League One rivals Exeter 4-1 at the Kassam Stadium. Walsall came from behind to beat Carlisle 2-1 with an 88th-minute Andy Williams equaliser and a stoppage-time goal from fellow substitute Douglas James-Taylor. The Sheffield Wednesday substitute Michael Smith hit two goals in six minutes in a 2-1 comeback win over Mansfield of League Two at Hillsborough, while Shrewsbury beat Peterborough 3-1 to also book a place in Monday’s draw. Colby Bishop scored twice from the penalty spot as Portsmouth came from behind to beat MK Dons 3-2 at Fratton Park. In Saturday’s late kick-off, National League Dagenham were denied another upset when Scott Kashket scored a stoppage-time equaliser for Gillingham at the Chigwell Construction Stadium after Josh Walker had put the hosts in front with just 10 minutes left.