The Cherry and Whites fell to a 12-10 defeat at Vicarage Road as Saracens booked a trip to Twickenham on May 28 for a Grand Final rematch against Leicester.
Owen Farrell kept his nerve in blustery conditions to land four penalties, including the decisive kick after Nicky Robinson's try had given Gloucester a late lead.
Gloucester's director of rugby Bryan Redpath conceded his side had been second best against a Saracens side adept at playing "risk-free rugby".
But Fuimaono-Sapolu was more forthright in a frank series of Twitter messages which could land him in hot water with the Rugby Football Union.
The Samoan tweeted: "I would say the referee was a joke but I'd probably get fined for it so I won't.
"Fair play Sarries. We score 20 more tries than them and the only try in the semi. Horribly boring but very clinical. Fair play.
"We scored two tries. One disallowed. No wonder my super15 friends are making jokes about northern hemisphere rugby. Boring rugby wins.
"The only semi-final that can't sell out!
"Farrell put more bombs on us than the U.S did on Osama Bin Laden."
Farrell took over the kicking duties after Richard Wigglesworth and Alex Goode had both missed early shots at goal and insists he is ready to take similar responsibility in the final.
"I would love to kick in the final. We will see how it goes in practice but I am always confident and I will be ready," he said.
However, Farrell was far from faultless. On a windy day he missed four penalty shots, two of which hit the post, and failed with two drop-goal attempts.
Gloucester took the lead with Robinson's breakaway try after Farrell's second drop goal effort had been charged down.
But the 19-year-old stepped forward to land what he later described as the biggest kick of his career to book Saracens a return to Twickenham.
Farrell's temperament was praised by Saracens director of rugby Mark McCall.
"It says everything about him that he missed a couple of kicks at goal and he is the guy who wants to put his hand up to kick the winning penalty," McCall said.
"He has been incredible for us over a six-month period. He has guided the team to this run of victories we have had and he did that again today."
Saracens were beaten by a last-minute Dan Hipkiss try in the 2010 final, but Farrell believes the squad have improved since then. They head to Twickenham on the back of a 12-match winning streak.
"I was involved in the final last year but we have grown as a team week by week this season," Farrell added.
"Leicester are an unbelievable team and very tough, but I know we will be confident and will just treat it as another game."
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