Both players were in the starting XI for the season opener at Old Trafford and Lukaku - a £75m signing from Everton - wasted no time in justifying his price tag by netting the first two goals as Mourinho's side ran out 4-0 winners.
"The Premier League taught me that you need to be adaptive to perform immediately," Mourinho told BBC Sport afterwards. "Both Romelu Lukaku and Nemanja Matic have years and years of Premier League experience, it is easy for them compared to Victor Lindelof, who needs time.
"Nemanja is top player with a top stability and we need that. Romelu is aggressive so they improve our team and the way we work. We have conditions to be a better team this season than last season.
"Romelu can gives us aerial threat, protect the ball and a good way out for us. I repeat, we are not on the moon but it is a good start. I enjoyed the confidence levels."
Next up for Mourinho's side is a trip to Swansea City for next Saturday's early kickoff.