Cricklade went into the break three up with goals from Ben Carter, Ian Ross and Adam Smith and held on in the second half to become the first giant killers of the cup this season.
Five minutes into the second half the home side's keeper Paul Warren pulled down a Purton forward in the box and Simon Pugh converted the penalty.
The Hellenic league side then had their best spell of the match and added a second when a good cross from Lee Jones was converted by Pugh.
Purton then hit the post when scoring looked the easier option late in the game after Cricklade missed further chances.
Cricklade boss Graham Jackson was very happy with the result and said : "We were superb in the first half, quicker on the ball and played some good football. Had we gone in at the break five up we would not have been flattered."
Hellenic Premier side Wootton Bassett were made to fight hard by Bromham before scoring in the last 15 minutes to run out 2-0 winners.
Bassett boss Pete Yeardley said: "A win is a win and we needed one badly, they battled well and made things difficult for us, at one stage I could see the tie going into extra time."
There were very few chances created in the first 45 minutes and the tie continued in the same vein until a strike by Andy Youngsam and another from Mick Byrne put the Hellenic side into the next round.
AFC Stratton were beaten 6-0 by Screwfix side Melksham Town, failing to match the home side in any department. Jamie Harrison (2), Jamie Cheeseman, Ollie Gee, Owen Bryan and Carl Harfield the scorers.
New College were beaten 3-1 at Westbury but impressed the locals with their brand of football.
The home side took a first-half lead with a strike by Steve Seals after a quarter of an hour and honours were fairly even for the rest of the half.
Scott Lane equalised for the College on the hour but two goals from Lee Carpenter and Lee Burns settled the Swindon side's fate.
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