Chris Brown's last-gasp goal cancelled out Mathias Pogba's first-half strike to take 10-man Alex to penalties.
But after Robbie Blake missed from the spot, Barker was quick to praise the amount of players that stepped up to take a kick.
"We practice penalties and we actually had seven or eight who wanted to take them, which is a rarity.
"It was great to see them wanting to step forward and they all took them very well - none of them looked like missing.
"It's a lot easier taking them on astro-turf at the training ground than on grass in front of crowds and there was pressure on them as it means something to go through to the next round."
Barker also added they would need to assess Matt Tootle's challenge on Blake but admitted they had been disappointed with referee Trevor Kettle's performance all night.
"We will need to see the sending-off again but we weren't too happy with the referee all night as a lot of bad tackles were going unpunished."