The League Two promotion hopefuls had more than held their own against a much-changed, but still strong, Villa team and created the better chances before Clark headed home with 15 minutes remaining.
Substitute Gana sealed a fourth-round home tie against Manchester City at the end of the month with a second goal in the final minute.
Salomon Rondon’s first FA Cup goal saw West Brom edge Bristol City 1-0 in their replay at Ashton Gate.
Rondon settled the tie 1-0 in Albion’s favour with only his fourth goal for the Baggies since completing a €16m move from Zenit last August. The Venezuelan had not scored since the end of October, but he lived up to his hefty price tag with a delightful 52nd minute finish after stealing between City defenders Aden Flint and Derrick Williams to control Craig Dawson’s cross.
“It was a scrappy game on a pitch that was freezing. But we’re through and we’re happy for Salomon too,” said Baggies defender Jonny Evans.
Mick McCarthy’s Ipswich bowed out to League Two side Portsmouth, who enjoyed a 2-1 win at Fratton Park.
Piotr Malarczyk tripped McNulty in the box — the first of two yellow cards on the night — and Gary Roberts gave Pompey the lead. Marc McNulty got the second, rendering a superb strike from Ainsley Maitland-Niles as consolation.
MK Dons secured a fourth round meeting with Chelsea by seeing off Northampton Town 3-0 at home.
Following a tense first half, the Championship side pulled away with two goals in seven minutes, the first through a Ben Reeves 51st-minute penalty. The League Two outfit’s hopes faded as Josh Murphy sped clear to tuck home the second and Simon Church converted an 89-minute penalty.
Beleaguered Bolton Wanderers can enjoy some brief respite from their financial woes after avoiding the embarrassment of bowing out to non-league opposition in last night’s replay.
Although Joe Partington nudged Eastleigh ahead, Gary Madine and Dean Moxey replied for the hosts.
Andy Drury kept the dream alive for Eastleigh when equalising on the stroke of half-time but Darren Pratley, whose leveller had earned the replay, buried Bolton’s winner on 58 minutes to seal a date with Leeds in the next round.
Huddersfield Town’s Irish goalkeeper Joe Murphy saw his cup ambitions crumble after Reading mounted a stunning comeback to win 5-2. Early goals from Jamie Paterson and Tommy Smith had Town cruising yet losing Jonathan Hogg to a straight red card unsettled them, allowing Lucas Piazon reduce the arrears before the interval.
Matej Vydra intensified the turnaround with a second-half hat-trick. Fernandez Iglesias hit to fifth goal to earn the Royals a tie against Walsall.
Elsewhere, Carlistle beat Yeovil 5-4 on penalties after a 1-1 draw while 10-man Bury beat Bradford 4-2 on penalties after a 0-0 draw.