Supremely organised and committed with a sprinkling of stardust, the Giants are unrecognisable from the team Watson inherited at the end of 2020.
There was a sense of inevitability about the result even before Josh Jones opened the scoring for the Giants.
Innes Senior lit Elland Road up with a stunning 90-metre try, only to see it eclipsed by Jermaine McGillvary's sensational slaloming effort.
The game was over as a contest long before referee Liam Moore confirmed Huddersfield's first Challenge Cup final appearance since 2009.
Watson's men will face Wigan Warriors at Tottenham Hotspur Stadium on May 28 and on Saturday's evidence are a team built for knockout rugby, giving them every chance of claiming the trophy for the first time in 69 years.
As the Giants build towards a trip to the capital, Hull KR will be wondering where they go next after a chastening defeat.
Tony Smith's gamble on the fitness of Kane Linnett - playing with a torn bicep - backfired with the back-rower forced off after just 14 minutes.
It was another worrying performance from a Rovers team still coming to terms with Smith's decision to move on at the end of the season.
The Robins did at least avoid the ignominy of back-to-back nillings thanks to Shaun Kenny-Dowall's late try.
With the dust still settling on a breathless first semi-final between Wigan and St Helens, the opening exchanges were played at breakneck speed.
Huddersfield - as they did in the round two Super League meeting between the sides - started on the front foot and suffocated the Robins.
The Giants fired an early warning shot when Rickey Leutele coasted over only to be pulled back for an obstruction in the build-up.
But such was Huddersfield's early dominance, it only delayed the inevitable.
The opening try came on 10 minutes with a helping hand from Rovers half-back Jordan Abdull, whose speculative pass inside his own 40 forced Kenny-Dowall into an error.
In the next set, Oliver Russell dummied his way past Ben Crooks and put Jones over under the posts.
Linnett was in clear discomfort during Huddersfield's early assault and it was no surprise when he went off clutching his injured arm.
It continued to unravel for the Robins as the Giants showed there is more to their game than simply grinding the opposition into submission.
With Rovers threatening from Abdull's cross-field kick, Leutele plucked the ball out of the sky with a sensational take and gave Senior the chance to race 90 metres to touch down.
Russell added his second conversion from in front and Huddersfield were in full control at 12-0 with 18 minutes on the clock.
The Robins improved in the second quarter but Watson's side were in the mood to defend.
The Giants comfortably handled everything Hull KR threw at them, which amounted to very little with the Robins failing to carve out a clear-cut opportunity in the first half.
There was a sense of panic from Rovers, typified by a pass into touch by Crooks from a scrum play close to the Giants line.
If Watson's half-time message to his Huddersfield players was "more of the same", he got his wish - and then some.
Four crisp passes gave McGillvary half a chance out wide and he needed no second invitation, seeing off Kenny-Dowall's tackle before skipping around Will Dagger and finishing under pressure from Ethan Ryan.
Russell missed his conversion attempt but the half-back was on target minutes later from a penalty to give the Giants an unassailable 18-0 lead.
Huddersfield sensed blood against an increasingly ragged Rovers and they landed another telling blow when Owen Trout crashed over next to the posts.
It was a case of damage limitation for the Robins with 24 minutes still left on the clock, a nightmare scenario in a semi-final.
Theo Fages rubbed salt into KR wounds when he slotted over a drop goal but Kenny-Dowall provided small cheer when he twisted his way over from Jez Litten's kick three minutes from time.
Huddersfield Giants: Lolohea, McGillvary, Cudjoe, Leutele, Senior, Russell, Fages, Hill, Levi, Wilson, Jones, McQueen, Yates.
Substitutes: Ikahihifo, Greenwood, Trout, Golding.
Hull KR: Dagger, Ryan, Crooks, Kenny-Dowall, Hall, Abdull, Milnes, Storton, Parcell, King, Hadley, Linnett, Minchella.
Substitutes: Litten, Sims, Keinhorst, Richards.
Referee: Liam Moore.