Cowell momentarily withdrew his ventriloquist mouth as he left the stage, having seemed very unhappy to be dragged into the act, his exit coming right after Tamley attempted to get him back on his feet to do the cancan.
He returned moments later to complete the act, but was quickly the subject of numerous angry tweets from viewers calling him “rude” for walking away.
Others have defended his decision and lambasted the artist for dragging him on stage.
One wrote: “Simon Cowell needs a sense of humor. How rude of him to walk away during a #bgt act.”
Another said: “You could literally see the artist panicking when Simon walked away. A little overreaction there Simon mate ?? Really inconsiderate and rude #BritainsGotTalent #bgt.”
“Did Simon just run away… seriously, how rude #BGT is,” someone else posted.
Others claimed Cowell “destroyed” the act by leaving the stage in the middle, as David Williams stood on stage without his counterpart.
However, some backed Cowell’s decision as he grew “uncomfortable” and called it a “televised moment of the year”.
Writer Matt Haig said: “No matter what you think of Simon Cowell, there is nothing more uncomfortable seeing someone being forced into a situation that makes them anxious. The involuntary audience interaction is obsolete and off-putting. ”
Many agreed with him, saying they found the act “shocking” to see Cowell becoming more and more “anxious” about being on stage.
As the judges settled back to give his opinion on Tamley, Cowell joked that the producers would be in trouble if they put him in the middle of an act.
Elsewhere in the semi-final, artist Graeme Matthews involved Amanda Holden in her act, taking her designer shoe for a “wash” as part of her performance.
Asked by Ant and Dec about the act on the results show, Tamley said, “This is the first time in my career that a model has left the stage on her own. He made herself a model, not me.”
Dance group Lil Icons, harpist Ursula Burns and magician Ben Hart were also hoping to make Sunday night’s final.
Britain’s Got Talent continues at 7:30 p.m. and 9:30 p.m. on ITV.