Barca were given special dispensation to sign former Middlesbough man Braithwaite this week, and he came off the bench to play a part in late goals for Messi and Arthur that put the pressure back on title rivals Real Madrid.
“Messi congratulated me, he’s a great guy and tried to make me feel comfortable on the pitch by passing to me often,” Braithwaite, 28, said.
“I’m very happy to have given my first assist to Leo.”
‘We’ve made an extraordinary signing’
Messi scored three goals in 26 first-half minutes before adding a late fourth from Braithwaite’s saved attempt as Barcelona moved two points above Real Madrid, who face Levante later.
After a slow start, Messi scored a sensational opener when he rounded off a brilliant solo run by chipping the ball over Eibar’s Marko Dmitrovic after 14 minutes.
As half-time approached, another quick burst of pace culminated in Messi firing a second low into the corner, and the Argentina forward converted from a loose ball three minutes later to kill the contest before the break.
Eibar continued to battle in the second half as both sides had goals ruled out for offside, but the hosts finished with a flurry as Messi capped a wonderful individual performance with his fourth three minutes from time and Arthur completed the rout.
Coach Quique Setien admitted he was surprised by the impact made by his new signing.
“Braithwaite did more than I expected, much more,” said Setien.
“Honestly, I think we’ve made an extraordinary signing. He will adapt perfectly to what we want to do, he was involved in two goals and he understands the game so well.”
Reigning La Liga champions Barca face Napoli in the Champions League last-16 on Tuesday, before travelling to the Bernabeu to face Real Madrid on Sunday.