Raith Rovers made Ross County manager Derek Adams pay for making sweeping changes by dumping the top-flight newcomers out of the League Cup.
Greig Spence opened the scoring for the First Division side from close range after 25 minutes.
Allan Walker set-pieces either side of the break led to headed goals from Brian Graham and Douglas Hill.
Graham fired his second of the night and ninth of the season after 63 minutes before Russell Duncan's reply.
Had it not been for former Celtic and Hibernian goalkeeper Mark Brown, making his debut after signing a short-term contract, it could have been a more heavy defeat for the Dingwall outfit.
Brown was one of nine changes made by Adams following Saturday's win over Dundee as he makes survival in the Scottish Premier League his priority this season.
Summer signings Jonathan Bateson, Mihael Kovacevic and Gary Glen were handed their debuts, while Paul Lawson, Martin Scott, Sam Morrow, Kurtis Byrne and Duncan came back into the side.
Rovers player-manager Grant Murray had made only one change from the team that drew 0-0 with Livingston, with Spence replacing midfielder Grant Anderson and the former Celtic striker had already threatened with an overhead kick before breaking the deadlock.
Graham slipped the ball through to Walker, who in turn teed it up for Spence for the easiest of tasks of guiding the ball into the net.
County had threatened first through a couple of Morrow headers and they responded to the goal with a stinging shot from Byrne that was held by McGurn.
Experienced Rovers defender Laurie Ellis hobbled off to be replaced with Colin Wilson on the half-hour mark, but the visitors were not put off their stride and Pat Clarke flashed a shot narrowly wide of the far post.
From Walker's inswinging corner, Graham sent a bullet header into the net at the near post four minutes before the break.
It got worse for County in the 51st minute when Walker swung over a free-kick from the right and Hill rose above everyone to head powerfully into the net.
With the Dingwall side in disarray, Walker's shot inside the box was blocked and Graham latched on to the loose ball and drilled it into the far corner of the net.
Brown denied Clarke with a fine save before Duncan prodded County's reply over the line after 84 minutes.
: "I made nine changes, but the players who came in didn't perform well enough.
"The players who came in tonight have missed a huge opportunity, they slide further down the pecking order.
"The players who had the jersey last Saturday, have the jersey for this Saturday.
"I gave the players an opportunity, we don't have reserve-team football now and had a squad that was more than capable of playing here tonight."
manager Grant Murray
: "We knew when the draw was made it would be a difficult game, but I can't give my players enough credit for the performance they put on tonight.
"We saw they had made changes before the game, but they still had experienced players in their team.
"I thought my players were magnificent. To go that well ahead against an SPL team, it was great for the guys, they truly deserved it.
"We knew they would come out in the second half and have a go and if they had scored then it might have been a different game."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.