The Vanarama National League South Rocks weren't going without a fight but after 150 goalless minutes, they finally found their goal touch.
A 3-0 win didn't quite tell the whole story but it's Ebbsfleet United who go on to welcome League One Doncaster Rovers in the first round.
McMahon says that tie is for the fans who have backed the club the whole way during an unconvincing first few months of the season and he told BBC Kent that it was the right result.
"They're going well in their league and only lost one game this season and we all know these games are tricky," he said.
"There's plenty of games have gone to extra time tonight against lower-division teams, they're always tough.
"It was very good performance. I thought first half we moved the ball really well, dominated possession and put them on the back foot and then second half more of the same.
"We looked a bit sharper as the game went on, created a number of chances and deservedly won. In the first half we were dominating the game as much as we are and there can be one counterattack and you're 1-0 down. Then everyone's depressed but the concentration levels were very good from the defenders in the first half."
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