Jurgen Klopp's team got their 2018-19 campaign off to a winning start on Sunday, thanks to Mohamed Salah's effort, Mane's brace and Daniel Sturridge's late goal.
Following the completion of his move from RB Leipzig this summer, Keita was handed his first English top-flight start and was later involved in the build up to the Reds' opening goal.
Pleased by the African star's outstanding performance, Mane backed the midfielder to get better for the Merseyside outfit.
“I’m happy for him. He played very, very well. Everybody was happy about the job he did for us,” Mane told club website.
“The beginning is not easy for new players, to learn about the guys. He will do better and better for us because he has great quality.”
“It’s a good time for us. Sometimes it’s difficult to start the season but we started very well in pre-season, we won almost every game," he continued.
"We have started the season great and everybody is happy. We’re going to try to keep the same level and keep going.
“We played great football today, we created many chances. We defended as a team, compact, and tried to win every battle. We scored four goals and we deserved to win.
“The most important thing was the three points and we got them, so we’re very pleased.”