The Staggies now need a victory against Alloa Athletic on Saturday to be sure of their place in the second round of the cup.
It was a miserable night for County, who unravelled after they had taken the lead through Billy Mckay midway through the first half.
A hat-trick from Arbroath’s Michael McKenna and a further goal from Kane Hester saw the Dingwall men come up well short, with Tony Dingwall also sent off for diving.
Despite the embarrassing nature of the loss, a victory against group leaders Alloa, who are two points clear of County, will ensure the Dingwall men progress to the second round as group leaders.
Team lines for our final Betfred Cup Group A match against @RCFCStaggies pic.twitter.com/IDuAhGsIv9
— Arbroath FC (@LichtiesNews) July 25, 2018
County were without defenders Marcus Fraser and Liam Fontaine through injury, with midfielder Iain Vigurs taking the armband in his first outing since returning to the Staggies from Caley Thistle during the summer.
There was also a debut for Stelios Demetriou and starts for youngsters Dingwall and Dylan Dykes, among six changes from the side that defeated Dundee United 1-0 last time out.
The Staggies survived an early penalty scare when referee Steven Kirkland booked Arbroath’s Mc-Kenna for diving after going to ground under close attention from Keith Watson just five minutes into the game. Arbroath continued to look dangerous, with Omar Kader hitting the post on 22 minutes.
The Staggies opened the scoring on the breakaway just 60 seconds later, with Dingwall slipping the ball through for Mckay to slot low under the dive of Darren Jamieson.
Jamieson was called into action to stop County profiting from a subsequent flurry, standing tall to deny Michael Gardyne following Vigurs’s through ball, before an even better save to block Mckay’s strike from a Ryan Dow delivery.
Those saves proved vital, with Arbroath taking advantage of the opportunity to draw level two minutes before the break. After Demetriou had felled Denholm, McKenna stepped up to calmly send Scott Fox the wrong way.
County were determined to regain their lead but were forced to do it the hard way when Dingwall was dismissed on 57 minutes after Kirkland showed him a second yellow card after ruling he had dived at the feet of McKenna in a bid to win a penalty.
Arbroath were instantly lifted and they took the lead from the resulting corner, with McKenna on hand to divert the ball home from point-blank range after Wallace had flicked on Denholm’s corner.
Arbroath 4 – 1 Ross County – a fantastic second half display against 10 men with (still being discussed) a hat-trick for McKenna and a fine solo goal for Hester pic.twitter.com/8cWUcqMuxs
— Arbroath FC (@LichtiesNews) July 25, 2018
The task was put beyond the Staggies when McKenna completed his hat-trick on 72 minutes but there was still time for worse to follow when substitute Hester rifled home on the counter-attack.
Arbroath (4-4-2) – Jamieson 6, Thomson 6, Gold 5 (Graham 46) Little 6, Hamilton 6, Whatley 7, Kader 7, McKenna 8, Wallace 7, Swankie 6 (McCord 77), Denholm 8. Subs not used – Linn, Graham, Hill.
Ross County (4-4-2 ) – Fox 5, Kelly 6, Morris 5, Gardyne 5, Mckay 6, Vigurs 6, Demetriou 5 (Lindsay 64), Watson 5, Dykes 5 (Draper 70), Dow 5 (McManus 46), T. Dingwall. Subs not used – Mullin, R. Dingwall, Paton, Munro.
Referee – Steven Kirkland 6
Attendance: 496
Man of the match: Michael McKenna.