Gini Wijnaldum had put Liverpool 1-0 up in the Welsh capital after a frustrating first half for the Reds.
Milner doubled the lead from the penalty spot after Salah had been brought down by Sean Morrison.
The 2-0 win meant Liverpool returned to the top of the Premier League, though Salah wasn’t happy that he hadn’t been given the chance to take the penalty.
Milner is Liverpool’s spot kick specialist, though hadn’t started the match against Cardiff.
Pictures show Salah picking up the ball having been fouled and appearing to want to take the penalty.
Milner is quick on the scene and attempts to grab the ball, though Salah does not let him have it easily.
After a few words are said, Milner walks away with the ball, leaving Salah visibly disappointed and angry.
Former England international Milner slotted the penalty home confidently securing Liverpool three points on a difficult afternoon.
The Reds are two points clear of Manchester City though Pep Guardiola’s side have a game in hand.
And Milner says Liverpool are going to keep fighting.
He said: “The boys have been tremendous all year.
“It’s not easy with the amount of games we’ve got, the pressure we are putting on City but we can’t do a lot more than that really.
“We’ve just got to try to be perfect between now and the end of the season, hopefully it’s good enough.
“If not, we’ve asked all the questions we can of City, we’ve lost one game all season.
“We are pushing them as hard as we can and you can see the strides this team has made over the last few years.
“The consistency, the ability, the way we can win games when we are not at our best and still in Europe as well.
“Hopefully we can keep pushing and finish the season with wins.”