Manager Duncan Ferguson questioned an offside call he felt denied Caley Thistle a win over Arbroath in the Premier Sports Cup.
Inverness drew 0-0 with their League One rivals at Caledonian Stadium in their penultimate Group D tie, but lost 5-3 in the bonus point shoot-out.
The result ended a 12-game losing streak for the visitors, extending back to March.
However, with ICT chasing the win, assistant referee Calum Doyle waved for offside when Billy Mckay looked certain to race through for a great chance to net.
Ferguson was less than impressed as his team now must beat Premiership Dundee on Saturday to stand any chance of reaching the League One second round.
The boss, who stressed this week that the League One kick-off is his priority right now, said: “We never seem to get a break. They said it was offside. I haven’t watched it back, but it looked onside to me, but the linesman put his flag up.
“That was a good spell for us. We played well and we also played well in the first half. That was a big moment for us.”
Inverness will round off their four-match League Cup group schedule on Saturday against Dundee in Brechin – with the Dark Blues in first place in the section after their 3-1 win over nearest rivals Annan Athletic on Tuesday.
ICT remain third in the group on four points and are three points behind Annan, so seven points would possibly not take them through to the knockout stages, even if they do defeat Dundee.
Inverness matched Arbroath over 90 minutes
Ferguson was full of pride that his mainly young side stood up to an Arbroath side tipped to be the League One champions come May.
He said: “We dominated the second half. They had gone down to 10 men (due to an injury, but we couldn’t break them down.
“It was frustrating as we couldn’t find our final pass. We were getting edgy and hitting passes that were not on.
“We should have kept possession better, but I was pleased with our overall game. It was such a young team, and I was really proud of them. Arbroath are the favourites for the league and we matched them.
“Dundee will be a big test for us. I’ll go with the same team and I’m sure we will acquit ourselves well.”
Defender Jack Walker, 18, suffered a head knock amid a penalty box collision late in the first half, leading to a lengthy stoppage.
Ferguson was waiting for an update, but initial reports are Walker is okay.
Four starting changes for Inverness
Inverness made four starting changes from their win over Bonnyrigg Rose, with Walker replacing injured defender Danny Devine.
Young trio Calum MacKay, Shae Keogh and Robbie Thompson also stepped up amid seven academy players on from the start.
Injury-hit Arbroath, with just three subs on board, were knocking the ball about with confidence, showing no hints of a side on a long losing run.
The collision in the box led to Walker receiving treatment on his head for several minutes just before the break.
He was replaced by Charlie Gilmour and Keith Bray filled the right-back void, with Jake Davidson going in as centre half.
The final opportunity of the first half saw Keogh’s effort, from a Remi Savage assist, saved by McAdams.
Offside decision denied ICT victory
At the start of the second half, Arbroath almost nudged ahead when, from a Callaghan corner, Thomas O’Brien headed just past the post.
The Angus team enjoyed a decent spell after this, with Inverness looking to link up play as they did so well on Saturday.
A strong Corner challenge on David Gold resulted in the Arbroath midfielder going off for many minutes for treatment before he had to concede defeat, meaning they played the final 17 minutes with 10 men.
Only sub keeper Robbie Hemfrey was remaining, but he was not pitched into action.
Then came the key moment where ICT could have clinched it.
A great ball from Longstaff found Mckay, but the raised offside flag caused anger on the sidelines and stands, with Ferguson venting his frustration.
Mckay went close late on when he shot over the crossbar just before substitute Cameron Ferguson headed wide after meeting Bray’s cross into the box in stoppage-time.
On it went to the shoot-out and a missed Longstaff kick was the only one not netted as Arbroath sealed the bonus point win shoot-out by a 5-3 scoreline.
Caley Thistle (4-4-2): Newman, Strachan, Walker (Gilmour 42), Savage, Davidson, Calum MacKay (Longstaff 46), MacLeod, Keogh (Corner 46), Bray, Brooks (Mckay 46), Thompson (Ferguson 71). Subs not used: Rebilias (GK), Nixon.
Arbroath (4-4-2): McAdams, Wilkie, Steele, O’Brien (Walker 60), Bisland, Callaghan, Gold, Slater, Spalding, Dow (Stowe 45), Murray, Subs not used: Hemfrey (GK).
Attendance: 754.
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