I was wondering if some athletes could manage to get the same performance or even experience a performance when not eating anything coming from an animal.
Are there effective athletes relying only on plants?
You certainly can be a world-class athlete on a vegan diet. For example, as of writing, the best weight-lifter in the USA, Kendrick Farris, is vegan. He keeps his critics quiet by breaking more records. Here are some other world-class athletes that are vegan:
This is really just a matter of 'let me google it for you'. The first hit yields a nice list.
Interestingly, there are endurance athletes as well as strength athletes.
Catra Corbett, ultra marathoner and general badass
Carl Lewis, sprinter, long jumper and multiple Olympic gold medalist
Brendan Brazier, iron man triathlete and author
Scott Jurek, leading ultra marathoner, trail runner and author
Kendrick Farris, Olympic weightlifter
Steph Davis, leading climber and base jumper
The Williams sisters, tennis professionals and multiple grand slam winners
Nick Diaz and Nate Diaz, two brothers, are MMA fighters in the Ultimate Fighting Championship. Nick is the former Strikeforce champion, and Nate has plenty of accolades of his own. They're two of the highest level fighters in the world. They also do marathons and triathlons.
They're usually pescetarian, but go full vegetarian during "fight camp", which is a ~6-8 week period of ramped up intense training before a fight.
Frank Medrano is a well known vegan bodybuilder.
I have to add one of my favorite ones to this list: Jermain Defoe, professional football player, currently a player of Bournemouth FC in the Barclays Premier League and who has credited his vegan diet as an important reason behind his top form despite his age.
He is also involved in different social causes and has his own charity foundation.