Keita opened the scoring after five minutes with his deflect shot, while teammate Roberto Firmino also tapped in from close-range in the first-half to secure a win.
Klopp said it was a "really, really good result".
He has scored 17 Premier League goals after 31 matches this campaign as the Anfield side are hoping to end their EPL trophy drought at the end of this term.
There is much excitement about the potential of the Brazilian centre-back, who cost the Spanish giants €50 million. The Liverpool midfielder still needed a touch of luck with his finish, though, as his shot deflected off Oliver Torres on its way past a helpless Iker Casillas.
Only a matter of centimetres denied Liverpool a third early in the second half when another excellent Henderson cross picked out Sadio Mane to volley home, but the Senegalese was flagged offside.
And, while Klopp would argue that the creativity instead comes from the full-backs - evidenced by another assist for young Alexander-Arnold here - Liverpool's lack of goals from midfield is nevertheless a weakness. There were some good moments in the game [but] obviously we can do better. Today he looked really good.
Depay has also been superb for his country's national team - scoring 16 goals and 12 assists from 46 global appearances. The first half is played and now we have a bit longer than 15 minutes to prepare for the second half.
Liverpool skipper Jordan Henderson was disappointed that they could not add to their tally after the break, although he was keen to talk up the importance of keeping a clean sheet. In stoppage time, with Liverpool looking worn out after their efforts throughout the game, it was Keita still charging forward, bursting past a couple of opponents into the box.
FW Divock Origi, N/R - The Belgian has played his way back into Klopp's thoughts and is getting fairly regular playing time of late. He obviously likes the position.
Keita put in arguably his best performance in a red shirt since joining in the summer and after a hard settling-in period appears to be fulfilling the faith Jurgen Klopp placed in him in agreeing a deal with RB Leipzig 12 months before he actually arrived.
As of writing, the market lists Liverpool as -470 favorites to advance to the semifinal while Porto can be found at +380 to pull off the upset.