Guinea international Keita joined Liverpool to much fanfare at the start of the season in a transfer that had been arranged several months earlier.
Technically gifted and forward-thinking, expectations were significant after a brilliant spell at RB Leipzig, but he has struggled to hold down a regular place in Jurgen Klopp's team.
Of his 22 Premier League appearances, only 13 have been from the start, though in recent weeks there have been suggestions he is finally settling into the side.
He scored his first top-flight goal against Southampton on Friday and he added to that with a deflected effort to open the scoring in a positive performance against Porto, and Van Dijk was thrilled for his team-mate.
"He's a fantastic player, we see obviously him day in, day out," the Dutchman told reporters at Anfield.
"I'm just happy for him. He's starting, but to score two goals in two games is very pleasing for him and very important for all of us."
Liverpool's performance at Anfield on Tuesday left plenty to be desired, as they wasted some presentable chances and allowed Porto opportunities that a better team may have capitalised on.
Van Dijk is adamant the tie is not over, highlighting the role that Porto's fans will be hoping to play in the return leg next Wednesday.
When asked if Liverpool are almost assured of progression, Van Dijk said: "Not at all, but it’s a good result and if we score one it's even more difficult for them to go through.
"We'll go there to play our game, hopefully we'll create chances and finish them off. It'll be tough because their fans are pretty extreme, like here, and I'm definitely going to enjoy that.
"Obviously, we go there looking to hopefully finish the job. We go to play our game, we don't go to defend, we go to attack because that's the way we've played all season."
Liverpool also played Porto in the Champions League round-of-16 last term, running out 5-0 winners after scoring all of their goals in the away first leg.
Van Dijk recognises Porto have come a long way since then, though.
"I definitely think so, especially better than last year away [in Porto]," he said. "I think they had a couple of injuries to big players and some changes, also we were clinical with our goals and maybe lucky, but they definitely improved and so have we.
"I think they [now] have experience, but also a lot of talent in the team, so they can be very dangerous on that front as well.
"Over there [in Porto for the second leg] they have big players back from suspension, we'll have one back. I'm looking forward to it."