WELWYN GC lost their last interest in a cup competition this season, when they were comprehensively beaten in this Dudley Latham Premier Cup quarter-final at Watford.
The Citizens' side were unrecognisable from the team that had demolished Leighton Town 5-2 the previous weekend, although injury and unavailablilty had forced manager Adam Fisher into several changes.
Central defenders John McGrandles and Martin Standen were unavailable due to work commitments and Ashley Kersey (ankle) injured, while Manny Melford-Rowe and recent returnee to the club, Juan Cifuentes were cup-tied.
Fisher shuffled his pack, Taishan Griffith returning to right-back and Jason Coughlan coming into central defence, while Josh Bronti and Luke Robins were back upfront.
WGC were stunned when they conceded their quickest goal this season, Sun scoring in the first attack of the match, big forward Kyle Johnson running from half-way past some half-hearted challenges to score with a shot past Jack Metcalfe that went in off a post.
The visitors tried to respond and when a Bronti cross was deflected to Jack Read, his underhit snapshot was straight at home keeper Matt Evans.
WGC had Nathan Dimmock, recently re-signed on dual registration from Royston Town, back in their colours and he got over a good cross-shot that Evans safely handled, but generally it was Sun who looked the livelier side.
The Citizens lost Coughlan with a recurrence of a calf injury on 25 minutes and had to re-shuffle again, Jay Welsh going to play alongside Yasin Boodhoo and Sean Brettell dropping in at full-back. Teenage midfielder Carl Chambers came on.
But both Chambers and Boodhoo were brushed aside by a determined run from Sun winger Jack Johnson five minutes from half-time, as he burst through to make it 2-0 at the interval, with a low shot beyond Metcalfe.
WGC introduced skipper Danny Payne after half-time for Ben Long, another injury victim and made a further change giving youngster Robbie Steedman an outing for Read.
Sun continued to force the pace and again Kyle Johnson got clear of WGC's ragged backline, to chip an effort wide when he should have scored.
A Robins overhead kick from a Griffith cross was WGC's best effort of the half before Sun wrapped up a semi spot when Jack Johnson again got in behind the defence and found the net for his second with a shot under Metcalfe's body in 72 minutes.
The keeper's unhappy half continued when six minutes later, Kyle Johnson's powerful shot was parried by Metcalfe, but the rebound ran straight to Sun substitute Adam Drakulic, who netted from a couple of yards.
Just when it seemed it couldn't get any worse for WGC, the dangerous Jack Johnson again got the better of their defence, rounding two defenders before attempting to go around Metcalfe. The keeper pulled him down, conceding a penalty and earning a red card from referee Trinder.
Yasin Boodhoo went between the posts, but faced a very weak spot-kick from Kyle Johnson that was straight at him and that he didn't even need to dive to save.
It was a rare moment of good fortune on a night to forget for the Citizens.
WGC: Metcalfe, Griffith, Boodhoo, Coughlan (Chambers 25), Welsh, Dimmock, Long (Payne 46), Brettell, Bronti, Read (Steedman 65), Robins.