The Catalan giants drew 1-1 against Celta Vigo in the first leg of their last 16 tie.
Messi didn’t play as he was rested, but Ousmane Dembele made a cameo appearance, coming on as a substitute in the 71st minute.
But it was Arnaiz when wrote himself into the history books.
After netting against Celta Vigo, it ensured he continued his perfect scoring record in Barca colours.
The winger has scored in each of his first three appearances for the La Liga powerhouse, with his treble arriving in 133 minutes.
And it is something that eclipses what Messi and Suarez have done for Ernesto Valverde’s side.
After showing his potential, Arnaiz could attract interest from other clubs across Europe, perhaps the Premier League.
The 22-year-old is believed to have a release clause worth £17.8million.
And Nou Camp chiefs will no doubt want to tie him down to a new deal soon to fend off potential suitors.
Barca host Celta Vigo in the return leg next Thursday (8.30pm).