Myles Weston had given the Gills a 42nd-minute lead at the Crown Ground on Saturday but Padraig Amond was caught by goalkeeper Stuart Nelson seconds after coming on as a second-half substitute, Nelson saw red and sub 'keeper Tommy Forecast's first job a minute later was to pick James Beattie's spot-kick out of his net.
"The result was a great result away from home," said Gillingham boss Allen, who will now be without Nelson for the Gills' FA Cup clash at Preston next weekend.
"The team gave everything, it was difficult in wet and windy conditions.
"We restricted the opposition, I am not sure about the sending-off as I was too far away but, with 10 men, we were still pushing at the end.
"It's a hard place to come, I have come here a few times with other teams and been spanked and it's been horrendous but we showed commitment and we have competed well.
"I thought for 70 minutes we were in control and they had possession but didn't get near our goal. Then they had a mad 10 minutes but we regrouped and near the end, even with 10 men, we looked like scoring but it's a hard place to come so we take a point."