CROESYCEILIOG left it as late as the seventh minute of injury time before a headed goal by Michael Dewer finally killed off Gwent rivals Llanwern in an incident-packed Nathaniel League Cup quarter-final clash at Woodland Road.
The MacWhirter Welsh League clubs looked certain to have to play an extra 30 minutes until Dewer leapt highest at the far post to head home a Jamie Jenkins corner past goalkeeper Chris Hart.
The crucial goal earned Croesyceiliog a 4-3 victory and a semi-final tie against Division One rivals Bryntirion Athletic at a neutral venue and a March date yet to be announced.
Jenkins' assist went a long way to making up for his first-half penalty miss during an opening 45 minutes when Caldicot referee Phil Bates controversially awarded three spot kicks - two to the home side.
Jenkins had struck the crossbar with a follow-up shot after Hart had saved his 13th-minute penalty, but Daniel Clouth soon made it 1-0 and when Dewer took over the spot-kick duties seven minutes later, it was 2-0.
Llanwern, though, gained a foothold when striker Steve Perszewski converted from close range and the Division Two visitors were level 11 minutes from the interval as the same players slotted home a penalty after Mike Vaux had been fouled.
And it was Llanwern who completed a fine comeback when Troy Quarterley put them 3-2 up on 57 minutes only for the home side to level just nine minutes later through teenage winger Josh Higgins.
As the visitors tired, having not played for three weeks, Croesyceiliog looked the stronger - although Dewar's late, late effort was an extremely cruel blow for manager Laurence Owen's men.
However, the former Caerleon player was gracious in defeat: "On reflection I think the best side won on the day and we looked like a team which hadn't played for three weeks," said Owen.
"We missed a great chance to score when we were 3-2 up, but those things happen in football.
"We both had our spells of dominance, but Croesyceiliog deserved to win over the 90 minutes."
Joint Croesyceiliog boss Neil Gilmore was a relieved man after Dewar's late show: "I thought the penalty miss was going to cost us big style, but overall I believe we just about deserved to win it," he said.
"It was a bit panicky when Llanwern came back from two down to lead 3-2, but we managed to recover ourselves.
"Llanwern are a good side and they'll go close to promotion if they can win their games in hand."
In the other half of the draw, Port Talbot-based Goytre United earned a semi-final meeting with Caerleon by winning 2-1 at Dinas Powys.
In the league, not one of the eight Gwent sides in action lost on a day when with Cwmbran Town without a game, eighth-placed Newport YMCA took the opportunity to draw level with the Crows on 25 points by winning 2-1 at Pontardawe Town.
After being level at 0-0 at the interval, YMCA led through goals from Craig Ford and Lewis Sommers before the hosts pulled one back five minutes from time.
"There's no doubt we deserved the three points because everyone worked very hard and we're delighted with the win, which was earned on a pig of a pitch," said YMCA boss Mark Coldrick, whose side have two matches in hand over Cwmbran.
One place below Coldrick's men are Caerleon, who also won 2-1 on their travels, at Bridgend Town, although manager Brendan Dowd was in North Wales running the rule over future Welsh Cup fourth-round opponents GAP Queen's Park.
Dowd saw the Wrexham-based side win 5-1 against visiting Cymru Alliance rivals Glantraeth and missed watching Chris Jones open the scoring, former Cwmbran Town and Newport County striker Raith Plant miss a penalty for Bridgend and Kristian Hanbury grab a last-gasp winner.
Caldicot Town's resurgence continued with a 3-1 home victory over struggling Maesteg Park Athletic with Gareth Cullimore, David Lloyd (penalty) and Craig Jones getting on the scoresheet at Jubilee Way.
"Only time will tell if we've turned the corner, but our recent form has been very encouraging," said Caldicot manager Jason Pritchard.
"We played very well and maybe could have scored a few more, although I'm just happy with the win."
In Division Two, a youthful Cwmbran Celtic side emerged 3-1 home victors against struggling Troedyrhiw - Kieron Porter, Luke Sallis and Rakesh Patel doing the damage.
"We did very well on a sticky pitch and managed to pass it around and get it out wide," said Celtic assistant boss Della Cheedy after watching his side move up a couple of places to ninth.
Tredegar Town are fast improving under new player-manager Andrew York and their latest outing resulted in a fine 3-1 win over visiting Briton Ferry Athletic.
Craig Burgess (2) and substitute Neil Matheson netted, with York later singing the praises of the latter.
"The game turned with the introduction of Neil Matheson, who certainly made a great impression," said York.
"The trick for us now is to continue our good form and not to get too carried away because there remains a lot of hard work ahead."
Tredegar's second successive win takes them up to 14th position and out of the relegation zone for the first time in months.
Risca United made it three games unbeaten, although their 1-1 draw at Porthcawl Town, where Mark Mears was sent off after putting his side ahead, failed to move them up from seventh position.
One team, however, who did push themselves higher was Goytre, whose 3-0 home success over Merthyr Saints puts them up one to tenth courtesy of an own goal and efforts by Rob Surtees and substitute James Wilkins.
Monmouth Town's home meeting with Cwmamman United and Aberbargoed Buds' away game at Severn Sisters were both postponed because of waterlogged playing surfaces.
At the very bottom, Abertillery Excelsiors, driven on by man of the match Matthew Lewis, gave themselves some sort of hope with a 2-2 home draw against Cwmaman Institute.
After falling behind early on, David Smith levelled for the home side, Lee Bull put them 2-1 ahead before the visitors grabbed a point with a long-range effort which goalkeeper Mike Price, who had earlier made a couple of tremendous saves, found too hot to handle.
l Caerleon can go above Newport YMCA and Cwmbran Town into seventh position in the MacWhirter Welsh League Division One table if they win Wednesday's rearranged game at Cambrian and Clydach on Wednesday, kick-off 7.30pm.
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