Mari joined the Gunners on a season-long loan from Brazilian side Flamengo in January, with the option to sign him permanently in the summer.
The 26-year-old has had to wait patiently for his first appearance, but Keown insists he looks a good prospect for Mikel Arteta’s side.
“He didn’t have a lot to do apart from his distribution, but he won everything when necessary,” Keown told Goal.
“You could see that he was a little bit short of fitness and that they are building him up. He looks to have the basis of a good player there.
“He wasn’t rapid, but he was quick enough to deal with all the situations. We were playing against a League One side who had a lone striker so he and David Luiz were able to boss him between the two of them.
“I think it was important that he had Luiz alongside him to talk him through the game. Now we have to give him time, he has to be given more opportunities.”
David Luiz was also impressed with Mari: “I’m so happy for Pablo, he’s a great guy, a great player and he had an amazing game so we are here to help each other and we are here, 25 players, ready to play, ready to play for Arsenal and ready to give the best job.”