Elton John did his best Taylor Swift impression in L.A. ... filling his concert with a ton of other stars.
Elton performed at The Wiltern Wednesday night and surprised fans with Shawn Mendes, Demi Lovato and Fall Out Boy frontman Patrick Stump ... all joining him for duets during the 3 hour show.
Our Elton sources say he handpicked the celeb guests from his music label.
Swift did the same thing at Staples Center last summer ... with the likes of Ryan Tedder, Mary J Blige, Kobe and Ellen DeGeneres.
Fun fact: Shawn, Demi and Patrick are a combined 71 ... Elton's 68 and still held his own.