THEY had just celebrated the 20th anniversary of one of Scottish football’s greatest shocks – a staggering and historic night at Celtic Park.

But Caley Thistle, reduced to 10 men for over half an hour, had to dig deep in hellish conditions to avoid suffering a cataclysmic upset of their own.

Graeme Murty’s sharp and impressive young set, featuring mostly teenagers and two over-age players – keeper Andy Firth and Jake Hastie – led in torrential rain through an early Dapo Mebude strike.

First half substitute James Keatings hit back just before the break, but took what looked like a ridiculous second yellow card for supposedly diving inside the Rangers box after 57 minutes.

It should have been a penalty for the Highlanders at 1-1, but they eventually did grab a lead through Miles Storey with 16 minutes left.

Then came a Rangers siege to the death, but the first Colts side to reach a Challenge Cup semi-final couldn’t prevent John Robertson’s men – the 2017/18 winners – reaching their fifth final.

There, they will meet Raith Rovers on March 28 or 29.

Home manager John Robertson was furious at referee Greg Aitken’s red card decision and the disallowing of a Tom Walsh finish, but happy to see his team survive the onslaught.

After television interviews, Robertson sent assistant manager Scott Kellacher in for post-match press interview, and he said: “We’re pleased to get there. It was a very hard game, against an excellent young team.

“A couple of big decisions in the game went against us and we’re hoping the authorities can look at the footage and rescind the Keatings red card because it was a disgraceful one – and James is gutted.”

Rangers, though, opening with the strong breeze and monsoon rain behind them, were quick and sharp – and soon troubling the hosts.

Within six minutes, the Ibrox side was in front.

Toshney tried to nod clear a long ball forward, but it fell to Jake Hastie who threaded a pass forward to Dapo Mebude.

The young Rangers prospect nicked it against Kevin McHattie’s heels before cutting a brilliant low shot into the left hand corner of the net from 20 yards.

Mebude had an incredible miss soon after, somehow lifting a six-yard finish square on goal against the crossbar from Kai Kennedy’s cross.

But the hosts, while never comfortable, grabbed a 44th minute equaliser.

Miles Storey beat Nathan Patterson for pace on the left and floated in a high cross, knocked back by the head of Jordan White.

There, 16 yards out, was substitute James Keatings hammering a low left foot shot inside the right hand post with Firth motionless.

Disaster struck the hosts after 57 minutes.

Storey cut the ball in from the left and James Keatings nicked in front of Ciaran Dickson and appeared to be tripped just inside the penalty area.

Instead, referee Aitken meted out a second booking and early bath for the home substitute.

The 10 men had the ball in the Rangers net ss Tom Walsh raced through to beat Firth, but the off-side flag was raised.

But the hosts’ moment came after 74 minutes.

Walsh cut back onto his left foot and curled in a fine cross met by James Vincent’s firm header.

Keeper Firth parried superbly, but Miles Storey pounce from six yards on the rebound.

Rangers continued to threaten in flashes with Kennedy striking the top of the bar from wide left amid heavy and sustained late pressure.

Ibrox development team manager Graeme Murty felt the whole experience of navigating games against Berwick, Stranraer, Ballymena United, Solihull Moors and Wrexham was one his charges could harness in the push for first team recognition.

Murty said: “I’m immensely proud. We could – and should – be sitting here as the first Colts team to reach the final.

“We were away from home against a quality team, second in the Championship, who have just knocked Premiership Livingston out of the cup.

“I’m here with a group who are, on average, 18 years old.

“This competition has been a fantastic experience for them and it’s up to them to take it on.”