Jesse Lingard showed his true colours to leave Antonio Conte red-faced with anger.
The ex-England international added to the Italian's growing frustration with a goal and an assist as the City Ground finally discovered what all the fuss was about. Lingard's arrival had been greeted as a statement signing during the summer as Forest beat West Ham to his signature.
But the former Manchester United man hasn't been able to even nail down a regular starting spot for himself as Steven Cooper's Reds struggled to adapt to life in the Premier League. Given his chance last night, however, he took it with both hands.
This cup tie had failed to ignite after a stale opening half in which only a Davison Sanchez clearance that clattered into the foot of the post off Forest striker Taiwo Awoniyi excited a boisterous crowd.
But all that changed when Lingard went the extra mile to poke the ball towards team-mate Renan Lodl, galloping forward on the left, five minutes after the break.
The Brazilian collected and cut inside Sanchez before bending a curler past Fraser Forster. Nine minutes later, Lingard took centre stage.
HAVE YOUR SAY! Who was man of the match as Nottingham Forest dumped out Tottenham? Comment below.
Forest broke from deep with Serge Aurier powering forward down the right. The full-back delivered a cross to the far post that was headed back into the danger zone by Sam Surridge and Lingard was there to glance home the second.
Conte was caught afterwards in an animated discussion with the fourth official - complaining about a foul in the build-up to the second goal while Lingard produced a little jig of his own as he celebrated with Forest's substitutes on the sideline.
Spurs were handed a lifeline in the closing stages when home midfielder Orel Mangala was dismissed after receiving a second caution for a scissor tackle on sub Richarlison.
But even that couldn't provoke the required response from the visitors.
Richarlison did head the ball home - but he was pulled up for offside.
And to further add to Conte's woes, Pierre-Emile Hojbjerg was substituted at the interval after coming under a crunching double tackle from Lingard and Lodl in the first half which will be worrying news for Denmark after the midfielder was named in Kasper Hjulmund's squad for the World Cup earlier this week.
Read more
Mirror Football's top stories
UEFA have not held back here...
Ferdinand honoured for his efforts
Mane's injury scare before the World cup
Southgate's squad reveal imminent