McNamara’s table-topping Dragons arrived at Headingley in outstanding form and having emerged as serious title contenders, but Leeds led 18-8 at half-time.
Yet the French visitors were not to be denied as three unanswered second-half tries from Matt Whitley, Mike McMeeken and Fouad Yaha maintained their position at the summit.
Australian half-back James Maloney was a key figure on his 300th career appearance and head coach McNamara said: “We were good in the second half.
“We were 10 points down at half-time and I wasn’t quite sure how we would react, but thankfully we reacted really well, so this was a different kind of win for us.
“We’ve played 14 games this season and 11 of them have been in England.
“It’s an incredible feat from the players and we will get back at four o’clock this morning and lose a full night’s sleep.
“But they just keep turning up and finding a way to win. We’ve got to ride this wave for as long as we can.”
Although French half-back Arthur Mourgue scored a fine individual effort to put the Dragons ahead, the Rhinos responded with scores from Rhyse Martin, Bodene Thompson and Liam Sutcliffe.
Yet Catalans showed their title pedigree after the break, despite losing prop Sam Kasiano to the sin-bin shortly before half-time, and ran in three more unanswered tries to seal the win.
McNamara added: “I thought Mourgue was pretty sensational with his running game, but Jimmy’s experience in that second half told.
“He knew when to kick the ball and what play to put on – he came up with some vital contributions, but that’s his job.”
The game was Leeds’ fourth in 13 days and boss Richard Agar admitted they ran out of energy in the second half.
The Rhinos had won their previous four games and Agar said: “In the first half we probably should have come in at least one score further up.
“In the second half, I would applaud the opposition. We can look at the schedule and our workload but the Dragons were really methodical.
“When they got a couple of chances, they executed really well.
“At the same time, there were some really poor elements to what we did during that period.
“But we couldn’t break that cycle because we couldn’t find the energy nor the field position to change the momentum of the game to get ourselves back in it.”