"I thought he played very well and I'm delighted for him," said Mackay.
"It's about Darcy coming back, kicking on and learning from his time against international teams and how international teams prepare and train.
"If he does that he'll kick on from here."
With Aston Villa's James Collins suspended, Wales manager Gary Speed selected Blake as Ashley Williams' central defensive partner against Montenegro
Blake retained his place for the England fixture and club boss Mackay believes his versatility makes him an important member of the squad.
"He's someone I see as being a player that can be adaptable," said former Scotland defender Mackay.
"That's a good thing to have, to be able to play in a number of positions because invariably it gets you in the team more often than not."
Blake's hopes of securing a regular spot in Cardiff's line-up have been hampered by a shin splint problem which he sustained during pre-season.
The Cardiff boss says Blake has worked hard to regain his fitness and is now pushing for a place in the staring line-up.
"I think Darcy's frustration was that his fitness levels when he came back and the injury he got stalled everything," added Mackay.
"He came back to pre-season and immediately got a knock which put him behind training wise.
"If you miss a chunk of pre-season [and] unless it's addressed then you're playing catch up throughout the season.
"When he came back from the knock it was addressed and he's someone I hope will really learn from good people around him in terms of how to look after yourself.
"For the last couple of weeks he's got some good fitness training and he's injury free so he's part of the squad again."